Adding migration to rename 'housing'... to 'housing-local-services'...

Renaming the tag 'housing' to 'housing-local-services' so 'housing' can be reused as a topic.

There is a Whitehall PR for retagging detailed guides (https://github.com/alphagov/whitehall/pull/1796) and a Router-data PR (https://github.gds/gds/router-data/pull/198) for redirecting the browse categories.
The `else` clause here will never be executed, because if `save!` fails, then an exception will be raised and the whole script will halt. Would it be better to remove the bang at the end of `save` here?