* Tidying up and documenting Tag model
Prior to this commit we had a custom `where(alias_for: [nil, ""])`
call. That call highlighted that we lacked a term for a Tag that was
not an alias. As part of this commit, I named that a "concrete" tag.
Further, I added scopes to assist in helping "name" those concepts.
This commit also adds a data migration and utilization of
StringAttributeCleaner to hopefully get away from `alias_for == ""`
situations.
As of writing this commit <2022-01-04 Tue 17:22 UTC>, in DEV.to we had 5
tags with `alias_for == ""`:
- actionshackathon21
- regex
- atlashackathon
- hotwire
- foremfest
In https://dev.to/admin/blazer I ran the following:
```sql
SELECT name FROM tags WHERE alias_for = ''
```
* Renaming concrete to direct
5b10addbb4