Add handout options

[froggleston]

This PR adds a new option in the config.yaml to support configuration of whether a handout should be included.

This removes the need to supply sandpaper.handout = TRUE in the options() function, but keeps the functionality to either specify handout: true or handout: "/path/to/handout_file.R"

[zkamvar]

I have no clue why the checks are not starting. @froggleston, could you merge in the main branch, add NEWS, and bump the version number to devel as described in https://carpentries.github.io/workbench-dev/releases.html?

[zkamvar]

I've added you to the DESCRIPTION and also fixed some tests that were breaking because of things.

At the moment Windows is failing for weird reasons:

  ══ Failed tests ════════════════════════════════════════════════════════════════
  ── Failure ('test-build_markdown.R:173:3'): Artifacts are accounted for ────────
  fs::path_file(a) (`actual`) and c(figs, b, "code-handout.R") (`expected`) don't have the same values.
  * Only in `actual`: "code-handout.R"
  
  
  [ FAIL 1 | WARN 0 | SKIP 24 | PASS 1005 ]
  Error: Error: Test failures
  ℹ 'D:/a/_temp/RtmpysTSvn/working_dir/RtmpEVreqL/file15c4ce49f6/lesson-example' successfully removed
  Error in vapply(X, FUN, FUN.VALUE = character(1), ..., USE.NAMES = USE.NAMES) : 
    values must be type 'character',
   but FUN(X[[1]]) result is type 'logical'
  Calls: test_check ... test_dir -> test_files -> test_files_serial -> <Anonymous>
  Execution halted

There are two things to notice:

1. the test failure is not actually a failure because it contains the value "code-handout.R"
2. There is a weird error coming from testthat itself. It will be worthwhile running the test-build_markdown.R test file in a windows environment (👋🏼 @klbarnes20) and see if we can reproduce the error.

[zkamvar]

I have finally figured out why the windows tests have been failing: there is a weird bug in gert where it's apparently having trouble removing a bare repository (that we use as the remote) because of a pack file with incorrect permissions:

  ℹ removing 'sandpaper-local' ('D:/a/_temp/RtmpuIca1V/working_dir/RtmpMr9uia/REMOTE-1a9826d69e4')
  ✖ Error trying to remove remote
  [EPERM] Failed to remove
  'D:/a/_temp/RtmpuIca1V/working_dir/RtmpMr9uia/REMOTE-1a9826d69e4/objects/pack/pack-07442ae371f99d1efb5939a0db60b2f13f1147c5.idx':
  operation not permitted

In any case, this is not going to be a big problem because this is explicitly in the context of tests and not in production code (i.e. we do not delete our remote in production).

[zkamvar]

Thank you @froggleston and @klbarnes20!