Fix Workhorse acceleration for encoded project IDs in API

All API endpoints support integer project IDs, but a number of others also support the URL-encoded form (e.g. group%2Fproject). For the sake of consistency, Workhorse should match on both integer and encoded formats. Endpoints that do not support the encoded form will return 400 whether they are accelerated by Workhorse or not.

I could be wrong about some of these, but when I started writing feature tests to cover this, I noticed NuGet returning 400 errors because the Grape API definitions were rejecting the :id. Here is the rundown:

Endpoint	:id supports encoded format?
/api/v4/projects/:id/packages/nuget	No
/api/v4/projects/:id/packages/maven	Yes
/api/v4/projects/:id/packages/generic	Yes
/api/v4/projects/:id/packages/conan	No
/api/v4/projects/:id/packages/pypi	No
/api/v4/projects/:id/packages/rubygems	Yes
/api/v4/projects/:id/issues/[0-9]+/metric_images	Yes
/api/v4/projects/:id/wikis/attachments	Yes

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/324814