Document allowed auth mechanisms for package managers

What does this MR do?

This MR documents which authentication tokens and transport mechanisms should be accepted by package managers. &3807 aims to redesign the authentication specification mechanism such that which tokens and transports actually are accepted can be easily determined by analysis (of Ruby). !50729 (closed) exhaustively tests (almost) every combination of token and transport in order to A) determine which are accepted and B) prevent regressions.

Currently, there is very little information on what tokens and transports should be accepted. I largely based the documentation on the description and discussion of &3807.

documentation Category:Package Registry devopspackage ~"group::package"

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