[CLOUDP-332196] Move Dockerfile for kubectl-plugin to cmd/kubectl-mongodb (#280)

# Summary

Since we [moved](#271)
the code for kubectl plugin to the dir `cmd/`, we also need to move the
Dockerfile there. This PR does the same and moves the Dockerfile to the
`cmd/kubectl-mongodb` dir.

## Proof of Work

Go to the root of the repo and run the below command to build the image

```bash
~/work/opensource/mongodb-kubernetes (move-kplugin-dockerfile*) » docker build -t viveksinghggits/mongodb-mc-plugin:0.0.1 . -f cmd/kubectl-mongodb/Dockerfile    vivek.s@M-HYXVRF7WDG
[+] Building 11.5s (10/10) FINISHED                                                                                                                              docker:desktop-linux
 => [internal] load build definition from Dockerfile                                                                                                                             0.0s
 => => transferring dockerfile: 309B                                                                                                                                             0.0s
 => [internal] load metadata for docker.io/library/golang:1.24                                                                                                                   0.7s
 => [internal] load .dockerignore                                                                                                                                                0.0s
 => => transferring context: 1.16kB                                                                                                                                              0.0s
 => [builder 1/4] FROM docker.io/library/golang:1.24@sha256:14fd8a55e59a560704e5fc44970b301d00d344e45d6b914dda228e09f359a088                                                     0.0s
 => => resolve docker.io/library/golang:1.24@sha256:14fd8a55e59a560704e5fc44970b301d00d344e45d6b914dda228e09f359a088                                                             0.0s
 => [internal] load build context                                                                                                                                                0.1s
 => => transferring context: 172.97kB                                                                                                                                            0.1s
 => CACHED [builder 2/4] WORKDIR /go/src                                                                                                                                         0.0s
 => [builder 3/4] ADD . .                                                                                                                                                        0.2s
 => [builder 4/4] RUN CGO_ENABLED=0 go build -a -buildvcs=false -o /go/bin/mongodb-multicluster                                                                                 10.4s
 => CACHED [stage-1 1/1] COPY --from=builder /go/bin/mongodb-multicluster /go/bin/mongodb-multicluster                                                                           0.0s
 => exporting to image                                                                                                                                                           0.0s
 => => exporting layers                                                                                                                                                          0.0s
 => => exporting manifest sha256:f0d3ef2864de3f81ec287382c66a76897419bddb5337a4e2fb9b56b7e3ca14dc                                                                                0.0s
 => => exporting config sha256:ce9089ec4e89d1b2c2b3dd5edeb4053eaae95c62a3182e7c015dd4d63ecf6be2                                                                                  0.0s
 => => exporting attestation manifest sha256:19f49f2aebd733e6a259441c81d0fef424c6af4fadf6f86e8032e77b7f1f3d51                                                                    0.0s
 => => exporting manifest list sha256:1574999c4354dbe1915980c0baf9aab438cbc59c7b909e34bf73b84ec98945e9                                                                           0.0s
 => => naming to docker.io/viveksinghggits/mongodb-mc-plugin:0.0.1                                                                                                               0.0s
 => => unpacking to docker.io/viveksinghggits/mongodb-mc-plugin:0.0.1                                                                                                            0.0s
```

## Checklist
- [x] Have you linked a jira ticket and/or is the ticket in the title?
- [x] Have you checked whether your jira ticket required DOCSP changes?
- [x] Have you checked for release_note changes?

Author: viveksinghggits

public/tools/multicluster/Dockerfile renamed to cmd/kubectl-mongodb/Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.24 as builder
+FROM golang:1.24 AS builder
 WORKDIR /go/src
 ADD . .
 

public/samples/multi-cluster-cli-gitops/README.md

@@ -13,10 +13,10 @@ To enable the manual disaster recovery using the CLI, this sample provides a [Jo
 The RBAC settings for the operator are typically creating using the CLI. In cases, where it is not possible, you can adjust and apply the YAML files from the [rbac](./resources/rbac) directory.
 
 ### Build the multi-cluster CLI image
-You can build a minimal image containing the CLI executable using the `Dockerfile` [provided in this repo](./../../tools/multicluster/Dockerfile).
+You can build a minimal image containing the CLI executable using the `Dockerfile` [provided in this path](../../../cmd/kubectl-mongodb/Dockerfile).
 ``` shell
 git clone https://github.com/mongodb/mongodb-kubernetes
-cd mongodb-kubernetes/public/tools/multicluster
-docker build . -t "your-registry/multi-cluster-cli:latest"
+cd mongodb-kubernetes/
+docker build . -t "your-registry/multi-cluster-cli:latest" -f cmd/kubectl-mongodb/Dockerfile
 docker push "your-registry/multi-cluster-cli:latest"
 ```