T7292: add build dependency python3-protobuf

[jestabro]

Used at build of python modules to autogenerate dataclasses from vyconf.proto.

Change summary

NOTE that this requires the following to avoid build errors, as described in https://vyos.dev/T7296:
vyos/vyos-1x#4426
It will remain in draft until the above is merged.

Add build dependency needed for autogeneration of dataclasses from the vyconf.proto file:
vyos/vyos-1x#4427

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

Related PR(s)

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

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[sarthurdev]

Makes sense why this package is needed based on the vyos-1x PR.