Support table prefixes in SQL storage backends

[jessepeterson]

Support dynamic table prefix specification in the mysql and pgsql storage backends. E.g. you can specify "mynano_" as the prefix and it would get prepended to the table names like "mynano_devices".

[jessepeterson]

As the other Nano projects seem to be drifting toward sqlc use, I imagine we'll migrate that direction as well for NanoMDM. That makes this issue rather difficult as sqlc does not have support for prefixed table names. Though it looks like there may be some steps in that direction in sqlc-dev/sqlc#3370.