refact(cmd): Encapsulate some functionality on Command and Server

This commit extracts 3 separate pieces of functionality into their own
function/method:

- Extracts the database opening with the intention to have a function
  that performs all that functionality but returns the created database
  object rather than setting it to the Server structure.
- Extracts database validation logic, to provide a common code path for
  upcoming functionality.
- Expose schema manager on the Command struct as well as providing
  common functions to acquire shared lock/close.

internal/cmd/commands/database/funcs_test.go

@@ -226,7 +226,7 @@ func TestVerifyOplogIsEmpty(t *testing.T) {
 	cmd := InitCommand{Server: base.NewServer(base.NewCommand(cli.NewMockUi()))}
 
 	cmd.DatabaseUrl = u
-	require.NoError(t, cmd.ConnectToDatabase(ctx, dialect))
+	require.NoError(t, cmd.OpenAndSetServerDatabase(ctx, dialect))
 
 	assert.NoError(t, cmd.verifyOplogIsEmpty(ctx))
 }

internal/cmd/commands/database/init.go

@@ -287,7 +287,7 @@ func (c *InitCommand) Run(args []string) (retCode int) {
 		return base.CommandUserError
 	}
 	// Everything after is done with normal database URL and is affecting actual data
-	if err := c.ConnectToDatabase(c.Context, dialect); err != nil {
+	if err := c.OpenAndSetServerDatabase(c.Context, dialect); err != nil {
 		c.UI.Error(fmt.Errorf("Error connecting to database after migrations: %w", err).Error())
 		return base.CommandCliError
 	}