Remove usage of *_STORAGE_API_ENDPOINT` environment variables for providers

[shreyas-s-rao]

How to categorize this PR?

/area security
/kind task

What this PR does / why we need it:
Remove usage of *_STORAGE_API_ENDPOINT` environment variables for providers, since credentials from secrets (including API endpoints) should not be passed as environment variables to the backup-restore container.

Which issue(s) this PR fixes:
Fixes gardener/etcd-backup-restore#727

Special notes for your reviewer:
/block
To be merged only after gardener/etcd-backup-restore#759 is merged, released and etcdbr version v0.30.0 is updated in druid.
For local testing purpose, I have included the PR build image from https://concourse.ci.gardener.cloud/teams/gardener/pipelines/etcd-backup-restore-master/jobs/master-pull-request-job/builds/37. This commit will be removed before merging.

@renormalize please let me know if we can pass domain to Azurite (with format http(s)://<storageAccount>.<domain>) instead of the entire URL.

Release note:

Remove usage of *_STORAGE_API_ENDPOINT` environment variables for Google and Azure providers. Storage API endpoint / domain will instead be directly consumed by etcd-backup-restore from the mounted backup secret.

[shreyas-s-rao]

/assign @renormalize @unmarshall

[renormalize]

As discussed off GitHub with @shreyas-s-rao, passing domain in the http(s)://<storageAccount>.<domain> format is supported by Azurite.

The way to perform this is to add:

127.0.0.1 account1.blob.localhost

to the hosts file of the host machine where etcd-backup-restore tests are running so that https://<storage-account>.blob.localhost resolves to the Azurite process. One simply needs to pass the storage account name that is configured to be used for Azurite, and the domain as blob.localhost.

However, it has to be kept in mind to not pass the disableProductStyleUrl flag to Azurite at startup. More can be found here.

Doing this will break the current way the Azurite make targets work in etcd-druid, so for a few commits Azurite will not be functional with etcd-druid for local development and testing.

[shreyas-s-rao]

Added this as a point in #782

[shreyas-s-rao]

/hold until gardener/etcd-backup-restore#759 is merged, released and etcdbr version v0.30.0 is updated in druid.

[ashwani2k]

/unhold as gardener/etcd-backup-restore#759 is merged.
@shreyas-s-rao Shall we merge it?

[shreyas-s-rao]

@ashwani2k I've removed the temp commit now, so the PR can be merged once the tests pass.

[shreyas-s-rao]

/test pull-etcd-druid-e2e-kind

[shreyas-s-rao]

@ashwani2k can you please raise a PR to update etcdbr image to v0.30.0 in images.yaml, along with the relevant release notes? I'm surprised that the PR was not raised automatically.

[shreyas-s-rao]

/test pull-etcd-druid-e2e-kind-nondistroless-etcd

[shreyas-s-rao]

@ashwani2k I have rebased the PR, so it can now be merged, after the tests pass of course.

[renormalize]

Tested with the v0.30.1 of etcd-backup-restore, and all behavior is as expected. Thanks.