[DEVREL-29] allow pretty permalinks to be handled for rest endpoints by default

[jazzsequence]

Fixes #178
Consolidates #181 into fewer commits

The linked issue is somewhat misrepresented. While the observed behavior is accurate (malformed URLs) it is not because of a misplaced /wp in the REST url -- WP-API URLs on Bedrock-based sites are expected to have two /wp/ strings in them -- one being the path to the application and the second is part of the actual wp-json/ URL (e.g. /wp-json/wp/v2/...). Therefore, the proposed solution would actually break sites without addressing the issue.

Since the issue only exists on newly created sites, the assumption here is that these sites are not using "pretty permalinks". Indeed, our tests assume permalinks are pretty for this very reason. In cases when "pretty permalinks" are not active, it makes sense that API requests might fail due to our URL rewriting for internal paths.

This PR works around the issue by simply accepting "pretty"-style API endpoint paths while also preserving the functionality of "plain" permalinks. Both "plain" and "pretty" permalinks are henceforth supported by the REST API for WPCM sites.

Tests are broken out into #182 so as to not mix release and non-release commits and will fail until this PR is merged.

Tests have been integrated back into this PR as well as other non-release changes. As a result, this PR MUST BE merged with a merge commit, not squash merge.

[github-actions]

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