[1.7.x] Fixed typos using https://github.com/vlajos/misspell_fixer

Backport of a71a2ea756 from master
[1.7.x] Fixed versionchanged indentation in docs/.

Backport of 5c517ec218 from master
[1.7.x] Added a warning about nonexistent FK constraints when unmigrated apps depend on migrated ones.

Thanks NotSqrt for the report; refs #23741.

Backport of f0ff452451 from master
[1.7.x] Fixed links to mysqlclient in database notes.

Backport of e0685368c6 from master