feat: module for IAM role to trigger deployments from GitHub actions

[FrontierPsychiatrist]

Adds a module that creates an AWS IAM role that can be used from GitHub actions with configure-aws-credentials to trigger deployments using the deployment module (by putting objects into S3 or pushing an ECR image).

---

Should I add an example or maybe even extend an existing example? E.g., in examples/deployment/complete the idea would be to have this:

module "github_role" {
  source = "../../../modules/github-actions-role"

  github_repository = "moritzzimmer/terraform-aws-lambda"
  s3_prefixes       = ["${aws_s3_bucket.source.bucket}/${local.function_name}"]
}

and in examples/deployment/container-image:

module "github_role" {
  source = "../../../modules/github-actions-role"

  github_repository = "moritzzimmer/terraform-aws-lambda"
  ecr_repositories  = [aws_ecr_repository.this.name]
}

[FrontierPsychiatrist]

This actually doesn't work as wanted when there's multiple / in the path...

[FrontierPsychiatrist]

Ah wait, no, this explicitly only wants the bucket part without any paths, so it's correct