fix: preservation of Tags assigned to CloudRun during deployments

[kartikangiras]

What this PR does:
It ensures tags assigned to CloudRun revisions stay preserved during deployments.

• Add Tag field to RevisionTraffic to support CloudRun revision tags
• Add GET method to fetch existing service configuration
• Tag Preservation Methods for fetching and merging
• Add Unit Tests to cross verify the code change is lgtm

Why we need it:
The problem was that when deploying new revisions, PipeCD was removing tags that were previously assigned to existing CloudRun revisions.

Which issue(s) this PR fixes:

Fixes #4954

Proof Manifests:

kartik@Macbook-4 pipecd % go test ./pkg/app/piped/executor/cloudrun -v -run "TestGetExistingRevisionTags|TestMergeTrafficWithExistingTags"
=== RUN   TestGetExistingRevisionTags
--- PASS: TestGetExistingRevisionTags (0.00s)
=== RUN   TestMergeTrafficWithExistingTags
--- PASS: TestMergeTrafficWithExistingTags (0.00s)
PASS
ok      github.com/pipe-cd/pipecd/pkg/app/piped/executor/cloudrun       1.260s

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[eeshaanSA]

Hey @kartikangiras, thanks for this! Was an issue opened for this?

We always advise opening issues first and discussing the problem before raising a PR. This OSS practice helps us keep things uncluttered.

Please link existing issue (if any), or create a new one. Thanks!

[kartikangiras]

Hey @kartikangiras, thanks for this! Was an issue opened for this?

We always advise opening issues first and discussing the problem before raising a PR. This OSS practice helps us keep things uncluttered.

Please link existing issue (if any), or create a new one. Thanks!

@eeshaanSA Issue #4954 was already listed, for which I have proposed this Pull Request.