fix: proto-linter compliance

[toumorokoshi]

Adding some fixes for the proto linter, to
re-enable it in CI and show it can be used to
validate AEP-compliant APIs.

[toumorokoshi]

Errors, with commentary:

# I can't get this to work by adjusting the HTTP URI. Including the path is a no-op for resources without a parent.
example/bookstore/v1/bookstore.proto:127:5:HTTP URI should include a `parent` variable. (buf-plugin-aep)
example/bookstore/v1/bookstore.proto:165:5:HTTP URI should include a `parent` variable. (buf-plugin-aep)
# looks to be an old aip linter issues.
example/bookstore/v1/bookstore.proto:178:3:Type must be UpperCamelCase with alphanumeric characters: "Book" (buf-plugin-aep)
# not sure about this one. Perhaps it doesn't like the dash?
example/bookstore/v1/bookstore.proto:215:3:Resource pattern "publishers/{publisher}/books/{book}/editions/{book-edition}" must alternate between collection and identifier. "{book-edition}" is not an identifier (buf-plugin-aep)
# more casing differences.
example/bookstore/v1/bookstore.proto:215:3:Resource plural should be lowerCamelCase: "bookEditions" (buf-plugin-aep)
example/bookstore/v1/bookstore.proto:215:3:Resource singular should be lower camel case of type: "bookEdition" (buf-plugin-aep)
example/bookstore/v1/bookstore.proto:215:3:Type must be UpperCamelCase with alphanumeric characters: "BookEdition" (buf-plugin-aep)
example/bookstore/v1/bookstore.proto:233:3:Type must be UpperCamelCase with alphanumeric characters: "Isbn" (buf-plugin-aep)
example/bookstore/v1/bookstore.proto:246:3:Type must be UpperCamelCase with alphanumeric characters: "Publisher" (buf-plugin-aep)