Refactor dbTool isConnected and add check for valid schemas

[broxen]

Segs/Utilities/dbtool/DBConnection_Helpers.cpp

Line 27 in df857b2

bool DBConnection::isConnected()

Refactor dbtool isConnected() and check for valid schemas:

• isConnected() should probably just verify that the database connection is "open" and may be as simple as m_db->isValid() (may avoid the segfault) and m_db->isOpen() regardless of the DB Driver;
• Create a new method hasValidSchema() (or whatever) to verify that the databases QT is connected to have been properly created with the SEGS schemas
• Check the schema version against latest migration to verify schemas are up to date, which dbtool already does in getDBVersion and getTableVersions.
• Expose version-check functionality to SEGSAdmin by command line switch.

This may resolve the Segfault on MySQL database creation that Mobby described in discord: https://discord.com/channels/242088237596803073/431572260692819988/1016553898577776660

This will help tee up SEGSAdmin for upgrade path workflow as described in #895

[broxen]

This will expose db checks to resolve #892 as well