chore: add linter for protobuf schema files

[jkowalleck]

we currntly do have linters for the XML schema.
we currntly do have linters for the JSON schema.
we currntly do NOT have linters for the ProtocolBuffer schema, don't we?

goal: introduce an automated tool chain, that can

• lint protocol buffer schema
  • find malformed schema files
  • find conflicts in field enumeration (duplicate use of a field number, etc ...)
  • optional but highly appreciated: detect breaking changes

this tooling should monitor

• all current (and future?) protobuff schema files in this repo's schema folder
  • glob schema/bom-*.proto

this tooling should run automatically on:

• each pullrequest
• each change in "master" and other relevant branches

the (github) workflow should be encapsulated standalone, not interfering any other/existing workflows

this tooling should be able to run locally

[jkowalleck]

a quick internet search found the following candidates for the job

• https://github.com/bufbuild/buf
  • as github action: https://github.com/bufbuild/buf-lint-action
• https://github.com/yoheimuta/protolint
• discontinued: https://github.com/uber/prototool -- they recommend https://github.com/bufbuild/buf instead

[jkowalleck]

while on it, it might help to add schema annotation to all the test resources(*.textproto)

spec: https://protobuf.dev/reference/protobuf/textformat-spec/#header

example:

# proto-file: schema/bom-1.6.proto
# proto-message: Bom

[jkowalleck]

all done via #385 and ff