(fix): HTTP error handling in VC API

[protocolwhisper]

Issue Addressed

Closes #4597

Proposed Changes

Eliminate all instances of Warp's "and_then" (which backtracks) and replace them with "then" (which doesn't perform backtracking).

Additional Info

No

[CLAassistant]

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[michaelsproul]

You also need to change the handlers themselves to return Response rather than Result<Response, warp::Rejection>.

Changing the definition of blocking_signed_json_task so that it uses something similar to convert_rejection (see my PR) would be one way to do it.

Try running make lint locally and getting it to suceed. You'll also want to rebase on unstable (your PR currently has conflicts because you started from stable).

[protocolwhisper]

@michaelsproul. I have just created a new PR #4606 following your guidance. I believe I have covered the necessary changes, but the make lint command is failing. Interestingly, the failures originate from other modules, specifically within consensus/types/src/, rather than the changes made in this PR. :)