Vendor in acts-as-taggable-on gem

Problem

We can't partition the taggings table as it is and we also want to add sharding keys to it.

Solution

• copy the gem files in the ./gems directory. bundle open acts-as-taggable-on could be used to access the files locally, but it doesn't include the tests.
• follow these guidelines for new gems: https://gitlab.com/gitlab-org/gitlab/-/blob/master/gems/README.md