Update Dockerfile for new fxconfig code path (#67)

<!--
Copyright IBM Corp. All Rights Reserved.

SPDX-License-Identifier: Apache-2.0

DELETE MARKDOWN COMMENTS BEFORE SUBMITTING PULL REQUEST.

If this PR introduces a breaking change that affects compatibility with
other components:
- The PR title must begin with the prefix [BREAKING].
- "Breaking change" must be included in the list below.
- Relevant stakeholders must be notified before or immediately after the
PR is merged.
-->
#### Type of change

<!--- What type of change? Pick one or more options and delete the
others. -->

- Updated `Dockerfile` for `fabric-x-tools` to use `fxconfig/cmd` as
path for building `fxconfig`.

---------

Signed-off-by: pco <pasquale.convertini@ibm.com>

Author: pasquale95

Dockerfile

@@ -10,9 +10,6 @@
 ###########################################
 FROM golang:1.25 AS builder
 
-# List of CLI tools to build
-ARG FABRICX_TOOLS="configtxgen cryptogen configtxlator fxconfig"
-
 # Build environment variables
 ENV CGO_ENABLED=1
 ENV CGO_CFLAGS="-D_LARGEFILE64_SOURCE"
@@ -27,10 +24,10 @@ RUN go mod download
 COPY . .
 
 # Build the binaries
-RUN mkdir -p /tmp/bin && \
-    for tool in $FABRICX_TOOLS; do \
-    go build -o /tmp/bin/$tool ./tools/$tool; \
-    done
+RUN go build -o /tmp/bin/configtxgen ./tools/configtxgen
+RUN go build -o /tmp/bin/cryptogen ./tools/cryptogen
+RUN go build -o /tmp/bin/configtxlator ./tools/configtxlator
+RUN go build -o /tmp/bin/fxconfig ./tools/fxconfig/cmd
 
 ###########################################
 # Stage 2: Production runtime image