[Tests] Support testing custom jobs (#86)

* chore: add support for testing custom jobs

* test: update testnet collections.json and jobs.json

* chore: cleanup

* chore: jobs fetching synchronous with delay

* chore: add utils

* chore: add more delay

* chore: reduce delay and remove XHTML job from testnet collections

* chore: reduce delay

* chore: revert collection changes

* chore: revert collection and testnet changes

* chore: support decoding general purpose data for POST jobs