Update compile-fixtures script to generate haddocks

[bolt12]

This PR updates the compile fixtures script to build the fixtures and haddocks at the same time using haddock. The script now also generates a single index.html file where one can see the haddocks of each individual fixture.

This PR also adds a new CI job that can be manually triggered, this CI job will essentially run some more comprehensive checks on top of the current ones, i.e. it will:

• Build the manual on all platforms for all LLVM versions
• Run cabal check for all packages
• Run cabal sdist and try to see if it is buildable for all packages
• Build haddocks for all packages

This PR closes #1159

Some nice features that would be nice to have: compile and generate haddocks for TH fixtures.

[bolt12]

hmm not sure if this needs to be merge in order for comprehensive-ci.yml to appear in the Actions tab.

[bolt12]

I have changed the comprehensive-ci.yml workflow to trigger on push so that I can see it works, then I will change to to workflow_dispatch type of event (See: https://docs.github.com/en/actions/how-tos/manage-workflow-runs/manually-run-a-workflow) so that it can be triggered manually from the UI