Adds field for using OIDC authentication to mount S3 buckets

[2022tgoel]

Describe your changes

• Provide Linear issue reference (e.g. MOD-1234) if available.

Backward/forward compatibility checks

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Check these boxes or delete any item (or this section) if not relevant for this PR.

• Client+Server: this change is compatible with old servers
• Client forward compatibility: this change ensures client can accept data intended for later versions of itself

Note on protobuf: protobuf message changes in one place may have impact to
multiple entities (client, server, worker, database). See points above.

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Changelog

• Adds a new oidc_auth_role_arn field to CloudBucketMount for using OIDC authentication to create the mountpoint.

[luiscape]

lgtm