Add /comments related errors and their integration tests

[oguzkocer]

Follows established patterns to implement error types for /comments and their integration tests. It also introduces CommentCreateParamsBuilder type to make it easier to build a CommentCreateParams type in Rust.

There is some discussion and pre-RFCs for using something like the ..Default::default() syntax for all the remaining fields when the type itself doesn't implement Default, but the remaining fields do. If such a feature is ever implemented, we could drop these builders.

There are also proc macro crates that implement these, but the ones I tried before didn't work out the way I'd like. For example, most build functions will return a Result<T, E>, but that only makes sense when the build might fail. In this builder type, I make the mandatory fields for the params type also mandatory for the builder, so we don't require any error handling.

In any case, I think this setup will serve us well on the Rust side for now. In native wrappers, this problem doesn't exist because we can use the #[uniffi(default = None)] macro attribute and both Kotlin and Swift can take arbitrary number of arguments in their constructor.

[crazytonyli]

@oguzkocer This PR's integration tests failed, and it caused the trunk branch and a few other PRs to fail.

[oguzkocer]

@crazytonyli Thank you for letting me know. I added the buildkite/wordpress-rs/wordpress-rust-wordpress-6-dot-6 task to the required checks, so that this won't happen again. I'll open a PR fixing the issue.