Integrate two workers into one ArchiveTraceWorker with pipeline_background queue. This queue takes loqer precedence than pipeline_default.

* processes any pending records which are not migrated yet
* bumps import_export version because of new commits_count attribute
* removes commits_count fallback method

Rinku 2.0.0 (the version we use) will remove the last character of a link if
it's a closing part of a punctuation pair (different types of parentheses and
quotes), unless both of the below are true:

1. The matching pair has different start and end characters.
2. There are equal numbers of both in the matched string (they don't have to be
   balanced).

Closes gitaly#1046

Part of the migration as tracked in: gitlab-org/gitaly#1026

A field didn't call the needed encoding helper, thus some UTF-8 encoding
couldn't be encoded to ASCII. Using the helper method this was fixed.

Tests are now run against Gitaly and Rugged too, to ensure both remain
working correctly.

Fixes gitlab-org/gitaly#1032, gitlab-org/gitlab-ce#43278