feat: add aws_gke_oidc_config and aws_gke_oidc_role modules

[amitchell-moz]

Add modules to provision AWS roles + OIDC configs to allow GKE workloads to assume AWS roles.

https://mozilla-hub.atlassian.net/browse/OPST-1509

This PR introduces 2 modules:

aws_gke_oidc_config
    creates an OIDC provider in AWS to setup a trust relationship between a cluster & AWS account
aws_gke_oidc_role
    creates AWS roles that use the trust relationship established by ^^ to allow GKE service accounts to assume AWS roles

These need to be separate modules because the OIDC provider URL must be unique per-account, but a given GKE cluster only has 1 OIDC endpoint. That means the OIDC provider tf must only be ran once, after that any number of roles can use it.

Changelog entry

add aws_gke_oidc_config and aws_gke_oidc_role modules

[github-actions]

Release plan

Directory	Previous version	New version
aws_gke_oidc_config	0.0.0	0.1.0
aws_gke_oidc_role	0.0.0	0.1.0

[amitchell-moz]

😿 I didn't realize my GHA bot commits weren't getting signed - the repo I tested on didn't require them. I'll need to get #240 merged, then recreate rebase this branch without the unsigned bot commits.