Make sure, when plugins cause a GET request to fail, there is always a response body.

[ywkaras]

Adds Au test with plugin forcing various errors on various hooks, with default body or set body.

[ywkaras]

As an alternative to HttpMsgComp.h, Alan proposes https://github.com/SolidWallOfCode/txn_box/blob/master/plugin/include/txn_box/ts_util.h / https://github.com/SolidWallOfCode/txn_box/blob/master/plugin/src/ts_util.cc

[ywkaras]

[approve ci centos]

[ywkaras]

Is this an incompatible change? Since plugin which may have generated empty response bodies in some cases will not generate non-empty response bodies?

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. Marking it stale to flag it for further consideration by the community.

[ywkaras]

[approve ci autest]

[ezelkow1]

[approve ci autest]

[ywkaras]

This was an ask from YCPI Prod. But, no point in fixing it if it's going to continue to rot in the Sun.