* Use the impersonator id to prevent these tokens from counting
against the impersonated user when limiting the users' total
of access tokens.
* When connecting using an access token with an impersonator
add the impersonator as a field to the tracing span that wraps
the task for that connection.
* Disallow impersonating users via the admin API token in production,
because when using the admin API token, we aren't able to identify
the impersonator.
Co-authored-by: Marshall <marshall@zed.dev>
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