PMM-7: Enable pmm3-client release repository in Dockerfile

This PR adds the command percona-release enable pmm3-client release in the else block of the pmm_psmdb-pbm_setup Dockerfile.

Changes Made:

• Added percona-release enable pmm3-client release && \ at line 73 in the else block
• This ensures the pmm3-client repository is enabled for release versions when installing specific PMM client versions

Context:

The else block (lines 72-78) handles installation of specific PMM client versions that match version patterns. By enabling the pmm3-client release repository before installation, we ensure the correct packages are available from the release channel.

Checklist:

• Explore repository structure and locate the correct Dockerfile
• Create branch PMM-7-enable-release
• Analyze the Dockerfile structure and identify the correct else block
• Add the percona-release enable pmm3-client release line in the else block (line 73)
• Verify the change is syntactically correct (Docker parsed Dockerfile successfully)
• Commit and push the changes
• Request code review
• Run CodeQL security check
• Complete the task