Docs: Add/Split "Server Read-only Access" section from "Configuring Your Artifact Repository" page

[agilgur5]

Summary

Per #12467 (comment) and #13425 (review), instructions for Server access should be split into its own section in the artifact repo configuration page called "Server Read-only Access"

Use Cases

As the Server is an optional component and only needs read-only access to artifacts, this should be split into its own section on this page. It can also be linked to from the Server docs ("Argo Server" page, which already links out a good bit).

Any sections with existing Server references and permissions should be split to this section. It can reflect the same page structure with sub-sections per artifact repository provider.

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[agilgur5]

We should also make some more notations about least privilege use:

• the Server role should be separate from the ones used by the Executor
• invert Delete permissions as optional for Artifact GC? per feat(artifacts): support ephemeral credentials for S3. Fixes #5446 #12467 (comment), it currently says "remove if you don't use" but it should probably be inverted for least privilege
• "Get" is needed for input artifacts, "Put" is needed for output artifacts. If you're not using both, these could potentially be split