feat: Add attrUnmaskAllowlist RUM config option

[andrewatwood]

Motivation

When masking is enabled, RUM automatically masks all data-* attributes to prevent data leakage and slim down replay frame payloads. However, some UI libraries use CSS selectors that target certain data-* attributes and values, which can lead to breakage of styles and rendering issues during replay playback. We need a way to maintain these styles during playback and this seems like a relatively straightforward way to do so.

I thought about making this a map of attributes and allowed values for each attribute, but wanted to keep the surface of the checks small. There may be some perf optimization needed for such a high-frequency check but tested this as a proof-of-concept locally and saw the results I was after, so just starting with this base implementation to get a temperature check on a feature like this.

Changes

• Adds a attrUnmaskAllowlist option to the RUM configuration
• Reads from this list when present to determine masking behavior for attributes

Test instructions

• Create an element with CSS rules targeting specific data-* attribute values (ie. data-state=open)
• Initiate a RUM session with replay enabled and no attrUnmaskAllowlist provided
• Verify that the replay does not render the intended styles due to masking the attribute value
• Update the config to include a relevant attrUnmaskAllowlist
• Verify that the next replay DOES render the intended styles due to preservation of the attribute value

Once again I will likely need integration test help as I'm unable to run suites beyond the unit tests.

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file