CCE-GH executable

[moxcodes]

Proposed changes

Add the combined GH-CCE executable. This also refactors the GH executable into a 'base' metavariables to avoid code duplication as much as possible.

Types of changes:

• Bugfix
• New feature
• Refactor

Component:

• Code
• Documentation
• Build system
• Continuous integration

Code review checklist

• The PR passes all checks, including unit tests and clang-tidy.
  For instructions on how to perform the CI checks locally refer to the Dev
  guide on the Travis CI.
• The code is documented and the documentation renders correctly. Run
  make doc to generate the documentation locally into BUILD_DIR/docs/html.
  Then open index.html.
• The code follows the stylistic and code quality guidelines listed in the
  code review guide.

Dependencies

• Cce gh executable interpolator utilities #2322
• New CCE utilities needed for CCE-GH executable #2319
• Setup databox action #2555
• Add phase bookmarks to Algorithm #3272
• Specify temporal_id for interpolation in interpolation target tags #3421
• Alter CCE interface managers for new changes to interpolation #3422

[moxcodes]

The CI failure here is most likely due to running out of memory on the github CI virtual machines, so this PR will have to wait until the DataBox simplifications are complete so that the build is less expensive.

[geoffrey4444]

Would anyone object to squashing this one?

[geoffrey4444]

Could you please fix the conflicts?

[moxcodes]

rebased on develop, fixed all the conflicts.
Cheers!

[moxcodes]

Rebased on develop and fixed conflicts

[moxcodes]

Now dependent on #2555, but the good news is that the optimizations in that PR are enough to get CI to run to completion on this one.

[moxcodes]

Rebased on develop, no longer dependent.
Cheers!

[kidder]

@geoffrey4444 @markscheel please look at

[kidder]

@geoffrey4444 @markscheel please look at

@moxcodes this needs a rebase

[moxcodes]

I've updated this now, and added a handful of commits that were necessary to fix changes in the interface logic from time stepping and interpolator changes. The new commits are:

Reorder Register phase to before self-start
Add optional template argument for sublists of StepChoosers
Relax constraints on source tags for Horizon
Use self-start specific interface manager during self-start
Use LTS in CCE regardless of whether it is used for DG
Remove duplicates when adding classes to factory creation 
Change CCE slab size after self start

I'm happy to split some of these smaller preparatory commits out into a separate PR if that would be easier for the reviewers -- I just thought I'd put them here to begin with, because they are all related to making the CCE system work in tandem with GH.

[moxcodes]

We're going to try to incorporate changes from #3355 and #3409 so that the CCE side doesn't need to do quite so much to change slab sizes after self-start.

[moxcodes]

On the plus side, due to the new dense output features, the CCE-GH executable will now support local time-stepping, and independently varies the step size.
However, it also required some significant refactors, so this PR is dependent again.

[kidder]

@knelli2 can this PR be closed or is there still something we haven't implemented yet?

[knelli2]

We have a GH+CCE executable now. We don't have a BBH+CCE executable yet, but it's unclear if we actually want that (except maybe for CCM). And that would be a whole separate PR anyways. So I'll go ahead and close this PR.