Add ir_ modifier

[ikreymer]

Description

The ir_ modifier serves content w/o rewriting, similar to id_, but does rewrite Location headers such that they can be followed, especially when loading in the browser.

Motivation and Context

To support loading resources w/o rewriting, while still following redirects.

Screenshots (if appropriate):

Types of changes

• Replay fix (fixes a replay specific issue)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added or updated tests to cover my changes.
• All new and existing tests passed.