relates to #21335
Enables the agent socket by default and updates docs to strike references to having to enable it.
The PRs in this stack change the MCP server that Tasks use to update their status to rely on the agent socket, rather than directly dialing Coderd with the agent token.
Default disable was a reasonable default when it was only used for the experimental script ordering features, but now that we want to use it for Tasks, it should be default on.
Refactors Agent instance identity to be a SessionTokenProvider.
Refactors the CLI to create Agent clients via a centralized function, rather than add-hoc via individual command handlers and their flags.
This allows commands besides `coder agent`, but which still use the agent identity, to support instance identity authentication.
Fixes#19111 by unifying all API requests to go thru the SessionTokenProvider for auth credentials.
Refactors our use of `slogtest` to instantiate a "standard logger" across most of our tests. This standard logger incorporates https://github.com/coder/slog/pull/217 to also ignore database query canceled errors by default, which are a source of low-severity flakes.
Any test that has set non-default `slogtest.Options` is left alone. In particular, `coderdtest` defaults to ignoring all errors. We might consider revisiting that decision now that we have better tools to target the really common flaky Error logs on shutdown.
* Adds agenttest.New() helper function
* Makes sure agent gets closed on test cleanup
* Makes sure you don't forget to set session token
* Sets the agent and client logger automatically
Spike Curtis