feat(anthropic): support user_id metadata tag

[emhagman]

Summary

Add tag support for metdata.user_id in Anthropic message calls (seen here https://docs.anthropic.com/en/api/messages#body-metadata) so that you can filter traces by user_id properly.

Currently anthropic.request.paramters contains a string of the dict which can't be filtered. Similar to user being tracked as a tag in openai.request.user but for Anthropic.

Risks

See PR comment; Removes user_id from anthropic.request.params based on how it's coded. If people have trace filters, APM Metrics, etc by looking for user_id in their string already, it would break that. We could keep it in there for legacy reasons if needed.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[emhagman]

This does remove it from anthropic.request.params, not sure if we should include it for legacy reasons in case anyone was using string matching here in their traces (@anthropic.request.params:"...") or if it's OK to change this.