Show 'synonymous' instead of all non canonical tags

Noncanonical tags encompass both unfilterable and synonyms.

There was already a column to show unfilterable tags only.

The 'noncanonical' column was showing unfilterables and tags that had been merged with synonyms (mergers).

Now there is a 'synonymous' column instead, which shows only non-canonical tags that have synonyms.
Merge branch 'refs/heads/master' into issue-1891-view-synonyms-only
Merge branch 'refs/heads/master' into issue-1891-view-synonyms-only
Merge pull request #1217 from CristinaRO/issue-1891-view-synonyms-only

Show 'synonymous' instead of all non canonical tags