Unblock delegated tb.dev authentication from Cloud

Customer friction:

Users who are launching runs from a hosted computation solution, such as Google Cloud, encounter significant friction in the existing auth flow, where the user must follow a URL and manually copy and paste a code via stdin on the uploading machine. While it's possible for the user to clone their personal auth token to the filesystem of the upload machine, there is a security risk wherein any user in possession of that token can then control that users' tensorboard data, and there is no recourse to revoke that token.

Proposed solution:

Deliver an API Key-style auth approach where the user may generate API keys, or revoke their access. See https://cloud.google.com/endpoints/docs/openapi/when-why-api-key for details.

Start by reviewing the existing authentication flow and the linked Google Cloud API-key guidance. Define how users generate and revoke keys for hosted uploads, replacing the manual stdin code flow while avoiding unrestricted personal-token access. Done means the proposed API-key workflow addresses both cloud launches and token revocation.