feat: run UCC in an isolated virtual environment (#436)

### Description

[Document with more
info](https://docs.google.com/document/d/1FqGxAY8onYWaTus0g5LbCQD9a8FGMn8-yIGMTLoea8k/edit?tab=t.0)

This PR allows to separate UCC from TA dependencies, in order to avoid
dependency conflicts.

UCC version may be specified in requirements_ucc.txt file. Then, the
action will install UCC in an isolated environment.

### Checklist

- [ ] `README.md` has been updated or is not required
- [ ] push trigger tests
- [ ] manual release test
- [ ] automated releases test
- [x] pull request trigger tests
- [ ] schedule trigger tests
- [ ] workflow errors/warnings reviewed and addressed

### Testing done 

1. Build of a TA (no `requirements_ucc.txt` added):
https://github.com/splunk/splunk-add-on-for-salesforce/actions/runs/17427842825/job/49479100399?pr=788
2. Build of a TA (`requirements_ucc.txt` added):
https://github.com/splunk/splunk-add-on-for-salesforce/actions/runs/17426742577/job/49475535585?pr=788

Author: kkedziak-splunk

.github/workflows/reusable-build-test-release.yml

@@ -571,6 +571,24 @@ jobs:
             poetry export --without-hashes --with dev -o requirements_dev.txt
             cat requirements_dev.txt
           fi
+      - name: Setup UCC
+        run: |
+          if [ -f "requirements_ucc.txt" ]; then
+            python${{ env.PYTHON_VERSION }} -m venv .ucc_venv
+            echo "Found requirements_ucc.txt. Installing UCC dependencies in an isolated environment"
+            ./.ucc_venv/bin/python -m pip install -r requirements_ucc.txt
+            export UCC_GEN="$PWD/.ucc_venv/bin/ucc-gen"
+          
+            if [ ! -f "$UCC_GEN" ]; then
+              echo "ucc-gen not found after installing requirements from requirements_ucc.txt"
+              exit 1
+            fi
+          
+            echo "UCC_GEN=$UCC_GEN" >> "$GITHUB_ENV"
+          else
+            echo "No UCC requirements file found, skipping UCC setup"
+            echo "Consider adding a requirements_ucc.txt file and place UCC requirement there, to avoid dependency conflicts"
+          fi
       - name: Get pip cache dir
         id: pip-cache
         run: |
@@ -650,7 +668,7 @@ jobs:
       - name: Build Package
         id: uccgen
         run: |
-          ucc-gen --ta-version ${{ steps.BuildVersion.outputs.VERSION }}
+          "${UCC_GEN:-ucc-gen}" build --ta-version ${{ steps.BuildVersion.outputs.VERSION }}
           if [ -f package.json ]
           then
             yarn