Implement ingress control distinguishing between GET and POST to eoapi/stac/collections

[j08lue]

We want to try out how we can use the IAM building block to add authorization to relevant methods in the STAC API Transaction Extension.

• Protect eoAPI's STAC API Transaction Extension endpoints #101

The first step is to achieve the following behavior on the eoapi/stac/collections endpoint, using the tools available in the IAM building block (KeyCloak, API Gateway, policies):

1. GET requests are allowed anonymously
2. POST requests require some form of authentication and authorization

Acceptance criteria

• A route has been created in the IAM building block that implements the above behavior