Allow configuring of basic authentication

[valentindeaconu]

With the runatlantis/atlantis v0.17.5 release, users are allowed to configure a basic authentication. The helm chart does not allow the livenessProbe and readinessProbe to add custom headers, so this PR adds support for both the creation of credentials and probes.

In this PR you will find:

• Updated values
• Updated README
• A secret resource holding credentials
• Modified StatefulSet resource to inject the environments required by the basic authentication configuration (ATLANTIS_WEB_BASIC_AUTH, ATLANTIS_WEB_USERNAME, ATLANTIS_WEB_PASSWORD)
• [Removed] Modified livenessProbe and readinessProbe to add a basic authorization header

Tested it manually, deploying atlantis in an EKS cluster.

Edit:
There's no need for livenessProbe and readinessProbe to add a basic authorization header since the bug was fixed in atlantis source code #1896, so the code was removed.

[JeffreyVdb]

Looks good to me. We are also in need of this configuration. environmentSecrets isn't something that can help us because that would mean we have to create a secret outside of the helm installation, which means that secret will not go away automatically when we helm chart is uninstalled.

[valentindeaconu]

Looks good to me. We are also in need of this configuration. environmentSecrets isn't something that can help us because that would mean we have to create a secret outside of the helm installation, which means that secret will not go away automatically when we helm chart is uninstalled.

You can avoid that by using the extraManifests field already supported by this chart. That's the way I deployed in the first place this feature, before creating this PR.

[JeffreyVdb]

Looks good to me. We are also in need of this configuration. environmentSecrets isn't something that can help us because that would mean we have to create a secret outside of the helm installation, which means that secret will not go away automatically when we helm chart is uninstalled.

You can avoid that by using the extraManifests field already supported by this chart. That's the way I deployed in the first place this feature, before creating this PR.

My colleague and I both missed that one 😅 Thanks for clearing that up, that's extremely useful to know for future reference. And thanks for the changes, that'll make our configuration a lot easier as well!