MM-14145: The config store Set will now Save automatically (#10377)

* MM-14145: The config store Set will now Save automatically

When UpdateConfig (and configStore.Set) is called in admin.go and
config.go, commonStore.Set now takes a store-specific persist function.
It uses that persist function to save the configuration automatically.

Removed: Now callers do not have to call configStore.Save or
app.PersistConfig, and those functions have been removed.

Possible downside: this means a "failed to persist config" error can now
be thrown during a app.UpdateConfig or commonStore.Set call. But
considering application code never really sets a config without saving
it (except in the test cases, which were testing that -- see below), it
seems fine to group these responsibilities.

Also removed: tests for 'set without save'. Since that can not happen
anymore, the tests are not needed.

* Removed Save completely, cleaned up formatting, joined save test with
set tests.

* fixed shadowed variable error

app/saml.go

@@ -65,7 +65,6 @@ func (a *App) AddSamlPublicCertificate(fileData *multipart.FileHeader) *model.Ap
 	}
 
 	a.UpdateConfig(func(dest *model.Config) { *dest = *cfg })
-	a.PersistConfig()
 
 	return nil
 }
@@ -83,7 +82,6 @@ func (a *App) AddSamlPrivateCertificate(fileData *multipart.FileHeader) *model.A
 	}
 
 	a.UpdateConfig(func(dest *model.Config) { *dest = *cfg })
-	a.PersistConfig()
 
 	return nil
 }
@@ -101,7 +99,6 @@ func (a *App) AddSamlIdpCertificate(fileData *multipart.FileHeader) *model.AppEr
 	}
 
 	a.UpdateConfig(func(dest *model.Config) { *dest = *cfg })
-	a.PersistConfig()
 
 	return nil
 }
@@ -128,7 +125,6 @@ func (a *App) RemoveSamlPublicCertificate() *model.AppError {
 	}
 
 	a.UpdateConfig(func(dest *model.Config) { *dest = *cfg })
-	a.PersistConfig()
 
 	return nil
 }
@@ -147,7 +143,6 @@ func (a *App) RemoveSamlPrivateCertificate() *model.AppError {
 	}
 
 	a.UpdateConfig(func(dest *model.Config) { *dest = *cfg })
-	a.PersistConfig()
 
 	return nil
 }
@@ -166,7 +161,6 @@ func (a *App) RemoveSamlIdpCertificate() *model.AppError {
 	}
 
 	a.UpdateConfig(func(dest *model.Config) { *dest = *cfg })
-	a.PersistConfig()
 
 	return nil
 }