Add Browser Resource Timing Event

[hectorhdzg]

This is to continue discussion in original PR #1943, thanks @Karlie-777 for your efforts, I will try to add comments for open questions/issues here.

Changes

Adds Browser Resource Timing events to the Semantic Conventions

Merge requirement checklist

• [x] CONTRIBUTING.md guidelines followed.
• [x] Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• [ ] Links to the prototypes or existing instrumentations (when adding or changing conventions)