Update Advanced routing guide to include Regex path matching example

[salonichf5]

Currently we only have examples of EXACT and PATHPREFIX path matching in the advanced routing guide.

Once this PR goes gets merged to main, we should update the guide to showcase an example of RegularExpression path matching.

Acceptance Criteria:

• Update the advanced routing guide with valid examples for RegularExpression path matching
• Update the gateway API compatibility doc

[sjberman]

We should also update our compatibility doc