Feat/14 api gateway with domain regional

[StarfishM]

Summary

closes #14 Our first try at implementing this didn't sufficiently work with the cp-api setup we have. The reason for this was that in cp-api we have the following setup:

• root CA: contipark-api.de is in us-east-1
• our api gateways are deployed in eu-central-1
• custom domains were using contipark-api.de directly as a cert, therefore the domains were all in us-east-1
• when we tested this in they-terraform we didn't run into this, as we simply happen to deploy to the same region for all things.
• in order to be able to enable mTLS we need to have the custom domain & apigateway in the same region
• solution: we create certs for the endpoints in the same region as the apigateway (DNS validation is still done via the root cert in the US I believe but this is handled by tf and aws), and then use these certs for the custom domains themselves

PR instructions

• temporarily deploy a lambda with Api Gateway with a domain (little heads up deployment will take some time as cert creation and validation takes a hot minute, somewhere between 1.30-4.40 min, sometimes it goes really fast... most times it does not)
• cd examples/aws/api_gateway_with_domain
• terraform init
• terraform apply
• in aws browser console navigate to Api Gateway settings, and select Custom Domain Names, or click here
• select the domain for the lambda you've just deployed
• select to edit in domain details section
• verify that you have the toggle to turn on mTLS
• go back one step to the details for your custom domain
• select edit in endpoint configuration
• verify that you are using the certificate your created (should have the same name as your custom domain)
• don't forget to destroy your deployment afterwards terraform destroy

I already checked if this is compatible with cp-api, but if you want to run a double check, you can simulate the scenario we have in cp-api, by changing where you deploy your gateway + domain + cert, by altering line 15 to "eu-west-3" in this file examples/aws/api_gateway_with_domain/providers.tf creating the scenario, where they-code.de has it's root CA in eu-west-1, and you deploy your gateway+plus cert + custom domain in a region differnt to that one.

• redo all the steps from above

The steps of acceptance

✔ I executed the PR instructions and everything worked.

✔ I checked the requirements for the ticket, and they are matching the PR.

✔ I am satisfied with the code and left annotations if I had some ideas.

[StarfishM]

only leaving this here and open, for when we need to create the pr for #13 , as that PR integrates all changes from here in a dynamic approach so that we don't loose the api gateway with domain module but only gain a new api gateway with domain mtls module.

[StarfishM]

can now be closed, as we've merged the branch dynamically implementing this.