Generate ToSchema generic bounds on impl instead of requiring it on definition

[oxalica]

Fixes #1078

#[derive(ToSchema)]
struct Signed<T> { .. }
/// generates
impl<T> ToSchema for Signed<T> where T: ToSchema /* <- introduced by this PR */ { .. }

• Each generic types now automatically get a ToSchema bound in where clause of generated impl blocks. Thus the user does not need to explicitly add ToSchema bounds on struct definitions.

• Attribute schema(bound = ..) is introduced for struct or enum containers to opt-out the automatic ToSchema bounds addition, by manually provide where clause bounds for the generated impl blocks. The attribute is inspired by serde(bound = ..).
  Eg. schema(bound = "") can be used to remove bounds in case of PhantomData types.

This PR is based on 61c98bb instead of master because master is already failing the test after the rc version bump (snapshot assertion failure in openapi_schemas_resolve_schema_references and friends). It does not conflict anyway.

[oxalica]

@juhaku Seems you are introducing some merge conflicts 🤔

[juhaku]

This looks pretty good: 🎉 Thanks for the patch.

I updated it a bit, mainly I fixed the tests and rebased it above the master.

However could you update the docs for the new functionality in /utoipa-gen/src/lib.rs for what is changed in ToSchema derive macro. Also add entry to the utoipa-gen/CHANGELOG.md to top most of suitable category of unreleased changes. Maybe under Added title.

[juhaku]

@juhaku Seems you are introducing some merge conflicts 🤔

Yeah, that was unfortunate, but fixed them.

[oxalica]

Updated docs and added CHANGELOG. Seems the doctest for utoipa-gen (cargo test -p utoipa-gen --doc) is failing on master. Just manually checked all failures are unrelated.

[juhaku]

Great, 🙇 🥇

[juhaku]

Updated docs and added CHANGELOG. Seems the doctest for utoipa-gen (cargo test -p utoipa-gen --doc) is failing on master. Just manually checked all failures are unrelated.

Right, yeah there might still be some of those, I'll fix them later on.