Add checks before removing old notes or params_yaml columns

[gbp]

Relevant issue(s)

Connected to #6949

What does this do?

Add checks before removing old notes or params_yaml columns.

Why was this needed?

If a re-user skips 0.42.0.0 upgrade notes then they could lose data. Add a check to ensure we prevent this.

Screenshots

> rails db:migrate
snip
== 20220902112339 RemovePublicBodyNotes: migrating ============================
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:

We can't run the RemovePublicBodyNotes database migration.

We have dectected PublicBody::Translation objects which haven't been
migrated to the new Note model.

Please deploy Alaveteli 0.42.0.0 and run the upgrade tasks:
https://github.com/mysociety/alaveteli/blob/0.42.0.0/doc/CHANGES.md#upgrade-notes

./alaveteli/db/migrate/20220902112339_remove_public_body_notes.rb:4:in `up'

> rails db:migrate
snip
== 20230127132719 RemoveInfoRequestEventParamsYaml: migrating =================
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:

We can't run the RemoveInfoRequestEventParamsYaml database migration.

We have dectected InfoRequestEvent objects which haven't been migrated
to the new JSONB params column.

Please deploy Alaveteli 0.42.0.0 and run the upgrade tasks:
https://github.com/mysociety/alaveteli/blob/0.42.0.0/doc/CHANGES.md#upgrade-notes

./alaveteli/db/migrate/20230127132719_remove_info_request_event_params_yaml.rb:4:in `up'