(exporterhelper): Add exporterhelper timeout policy support

[jmacd]

Description

Second half of #11183.

Existing behavior is unchanged which is to sustain the short timeout, let it succeed if possible.

Alternative behaviors:

• "ignore": Ignore the short timeout, use the configured timeout
• "abort": Abort the request, since there is a chance the client will abort before we return.

Note: depends on #11387, has to be rebased. See also draft/discussion in #11198.

Link to tracking issue

Fixes #11183

Testing

New tests for 3 policy variations and that default is unchanged.

Documentation

✅

[jmacd]

This is a complete PR, so I am opening it for review.

However, I've added a new package config/configtimeout and it appears to break things if I try to add a new package and use it in the same PR (or same release). Therefore, I'm looking for feedback on the PR while in parallel, I'll send the new configtimeout package as a stand-alone PR.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[jmacd]

I am working on an RFC for this.