Update go-mssqldb driver reference

Notable changes:

Replace denisenkom/go-mssqldb to a maintained compatible microsoft/go-mssqldb driver;
Add azuresql alias.

With this change we only replace the driver and add azuresql alias for compatibility with xo and dburl modules.

To connect to MSSQL DB via Azure AD we need to import the submodule azuread. We could potentially replace microsoft/go-mssqldb with microsoft/go-mssqldb/azuread as it implicitly imports the root module and doesn't seem to have any bad implications. However, I'm not sure if it's a good idea, or we'd better treat azuresql differently.

It also might be a separate PR to keep the scope small.

References:

https://github.com/xo/dburl/pull/21

xo / usql

Update go-mssqldb driver reference #365