feat(rust-client): Implement many API using batch endpoint

[lcian]

Adds a many API that submits batch requests to the server.
The API is called many to indicate the fact that this can be interpreted as just a "hint" to use batching, but a many request from the user's pov doesn't necessarily map to a single batch request to the server.

This is a nice API when creating the requests but not so nice when retrieving the results, as the user will need to deal with wrapper types and different error types as well.

It should be kept in mind that most of the usage we expect here is from sentry-cli uploading multiple files. It's therefore quite unlikely that the user wants to inspect the result wrappers or anyways match on the errors, they most likely just care to know if all operations succeeded or not.

Motivated by the above reasons:

• I introduced a error_for_failures function that's useful if you just want to know if all ops succeeded or not
• As users are most interested in PUTs when using this API, I haven't thought about streaming the results of GET responses. We're just buffering the whole batch response with this implementation.

[lcian]

@sentry review

[github-actions]

Semver Impact of This PR

⚪ None (no version bump detected)

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[lcian]

@sentry review