Install stac-auth-proxy helm chart to handle auth for eoapi

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Depends on #97

Once we have eoapi upgraded to the latest version, we need to add Argo config to deploy the stac-auth-proxy helm chart on the cluster.

So the steps would be:

• Do Update montandon-eoapi to latest version of eoapi helm chart #97
• Configure eoapi to turn off external ingress and have it exposed only within the cluster via a Service
• Configure and deploy stac-auth-proxy - using the GO well-known auth config, and proxying requests to the internal STAC service.

We've tested the individual pieces here, so this should be relatively straightforward once we've done #97. Am happy to take this on.

cc @emmanuelmathot @geohacker @sunu @thenav56

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To get the steps down for this a bit more fleshed out:

• Create the ArgoCD application YAML, stac-auth-proxy.yaml or so in https://github.com/IFRCGo/go-deploy/tree/develop/applications/argocd/staging/applications
• For testing, it maybe useful to first point an arbitrary domain at the auth proxy instead of using the current eoapi staging domain name, so:
• First, just add stac-auth-proxy.yaml, add env vars for the go-api token configuration pointing to the GO openid-configuration and point some arbitrary domain to test pointing to the proxy, to verify that it all works.
• Once that works, disable external ingress on montandon staging and allow access only through stac-auth-proxy (point current montandon staging domain at stac-auth-proxy and disable ingress on montandon-eoapi).
• Test. If all is fine, create production stack.

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This is all done! Will close the ticket once it's deployed fully to staging and prod.