[BUG] Experimental: Namespacing of `MTA` Resources should be optional

[stotz89]

Describe the bug
Currently, the MTA Provider always uses a namespace (default if not provided). See here. If you want to update an already existing MTA which was for example deployed by the CLI without a namespace you are not able to do so and the deploy job runs into a conflict.

Tested with Provider Version
experimental

To Reproduce
Steps to reproduce the behavior:

1. Deploy a MTA using the CLI without a namespace
2. Try to update this MTA using CO and the MTA resource

Expected behavior

• If I don't want to use namespacing for apps/services/etc. I should have the option to do so in the MTA resource.
• Already existing MTA will be recognized by the Deploy Service and the will be updated.

Workaround
Explicitly add namespace: "".

Screenshots

Additional context
no further context

[Lasserich]

Thanks for taking care! I just saw this is on a separate branch then our main PR.
Maybe you can also merge it with this one? :)
#5