Use github actions instead of travis

[cderv]

• Using r-lib/actions as template
• Windows Linux and MacOS
• We won't publish to XRAN - could be added later

Todod

• Add a workflow to test knitr-examples - same as it is working now.
• Debug knitr-examples workflow

Idea

• It would be great to cache package installed for knitr-examples. It is currently 9 minutes.

[cderv]

Status & Progress:

We got this after knitr-examples checks

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   025-engine-ruby.md
	modified:   027-engine-bash.md
	modified:   042-highlight-matlab.tex
	modified:   098-highlight-python.tex

• 025 example is not working because Ruby throw deprecated warnings (https://github.com/yihui/knitr/pull/1920/checks?check_run_id=1414097721##step:11:2657) - fixed by 1195018 (#1920) - fixed in
• 027-engine-bash is failing because other engine docs have changed - modified examples in Some tweaks for GHA knitr-examples#73
• highlight examples have changed - don't know why. Something is different with highlight in GHA compare to travis - Should we update the examples ?

Other failure are the one we found on Travis too :
https://travis-ci.com/github/yihui/knitr/jobs/432589388#L2759

	modified:   009-slides.md
	modified:   010-upload.md
	modified:   021-ggplot2-geoms.tex
	modified:   046-read-rforge.md
	modified:   093-knitr-asy.md
	modified:   106-polyglot.md

But they do not put the job in failure.

[cderv]

On other note, I also removed some apt installation that where not needed (maybe they are already available in the runner)

• The dev dependencies for packages are now found automatically by remotes::system_requirements("ubuntu", "18.04")
• Some tools are already installed like cargo, ghc, texinfo.

There is only qpdf that does not seem to be installed already but was not required.

[cderv]

It would be better to merge this after merging knitr-examples, which I can't do myself.

Next step would be

• Do we need to fix highlight example ? Should we modify the resulting .md file due to the change we are seing in output ?
• Merge change in knitr-examples once ok.
• Modify the checkout of master in knitr-examples in the workflow in this PR
• Merge this PR in knitr.

[yihui]

The highlight examples have been updated: yihui/knitr-examples@0262a05

Thanks!