Add comment ignores to example

[SpencerC]

buf's allow_comment_ignores functionality does not work out of the box. It requires the bazel --experimental_proto_descriptor_sets_include_source_info to work. See: bufbuild/rules_buf#64 (comment)

Many of these changes mirror bufbuild/rules_buf#80, and I suspect adding them here as well will save a lot of folks needing to dive a layer down to figure out how to configure buf correctly.

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Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: yes
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: no

Test plan

• Manual testing; please provide instructions so we can reproduce: I'm guessing the behavior of the example directory is tested manually. To test, I suggest modifying the items in example/buf.yaml and the comment ignores in example/src/file.proto and verifying they behave as expected.

[CLAassistant]

All committers have signed the CLA.

[alexeagle]

neat thanks!

FYI @perezd - I suspect a lot of Bazelers will use Buf via this ruleset, and maybe you'd like to reduce the ambition of rules_buf if you can avoid maintaining formatting&linting support

[perezd]

Yeah, we would like to not maintain that. Sounds good to us!