[DOCS]: complete ProtoBuf schema annotations/comments

[jkowalleck]

the protobuf schema needs to be revisit,
and where missing, some documentation annotations need to be added.

the documentation should be taken from JSON schema file, as it is the textual equivalent to the human-readable specification.

to keep docs mandatory, enable the linter rule "COMMENTS" (except for legacy schema files)

• see https://buf.build/docs/lint/rules/#comments
• linter config: https://github.com/CycloneDX/specification/blob/master/tools/src/test/proto/buf_lint.yaml

[jkowalleck]

i work on this ASAP