move to using our own / forked versions of concourse resources

[gumaerc]

Currently, we are using a number of 3rd party Concourse resources:

• jgriff/http-resource
• ghcr.io/cludden/concourse-keyval-resource
• governmentpaas/s3-resource
• arbourd/concourse-slack-alert-resource

We should, at a bare minimum, fork these repositories and point to those forks in our pipelines. These repositories do not have a lot of stars, are controlled by 3rd parties and could be removed at any point. By forking them, the repository will only go away if we remove it and we have greater control over the code.