Description:
This PR is a new implementation of the switchover code that can be executed from the UI, replacing the need to run & connect from the command line.

A new make start-swo command has been added to the Makefile to locally start GoAlert in switchover mode.

• added sqlc for type-safe prepared statements
• added start-swo make target for starting in switchover mode
• removed obsolete contextLocker from app
• moved application name logic into the swo package
• moved all switchover-mode DB connection logic into swo.Manager
• dropped the switchover-shell subcommand
• dropped the now-obsolete pauseHandler
• added swoStatus query
• added swoAction mutation
• switched limit reset from truncate to delete from to be compatible with swo
• added switchover_log table for traceable coordination of the swo
• added a db_id column with a unique ID to validate DB URLs are correct
• removed old switchover test
• removed legacy switchover package
• added swo and related packages
• Moved DB connector logic to util/sqldrv with the RetryDriver
• added new Switchover page to admin

Which issue(s) this PR fixes:
Closes #2506

Screenshots:

Describe any introduced user-facing changes:
A new Switchover page is now available in the admin section.

Describe any introduced API changes:
A new query and mutation was added to allow starting SWO.