* Refactor schema table migration mechanism
The old schema table migration code was initializing the migration
engine before changing the migrations table and was mixing queries on
two different database connections (the `s.db` connection and the
migrations `db` connection).
The changes on this commit take care of changing the migrations table
before the morph migration engine is initialized and they use the same
connection for all operations, better isolating the schema table
migration process.
* Update migrate function to take the cluster mutex first thing
* Split migration code and orchestration on different functions
* Wrap custom errors on data migrations
* Rename private migration method
* Update server/services/store/sqlstore/migrate.go
Co-authored-by: Doug Lauder <wiggin77@warpmail.net>
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