WIP: Adds run operation for harvest plan entities

[paul-m]

Fixes [issue#]

This is basically a proof-of-concept where I teach myself how to wire up entity operations.

Todo:

Prettify the harvest_run entity display.
Handle a bunch of error cases.

Discoveries:

Harvests can be 'reverted', which unpublishes the dataset nodes in various ways. This is different from reverting an entity revision, which is where you go back to old content from a previous edit. Drupal's entity system wants us to use 'revert' to mean the latter rather than the former. I got it working by callling it a rollback instead, but that's probably up for discussion.

Many permissions use an '[operation] [entity]' name, such as 'edit node', but the entity access system wants permissions to have a name like '[entity].[operation]', such as 'harvest_plan.run'. We'll need to rename permissions somewhere.

Demo:

Make a local.
Enable and create sample content.

ddev drush pm-enable sample_content
ddev drush dkan:sample-content:create
ddev drush cron
ddev drush cron

Visit the harvest page: https://dkan.ddev.site/admin/dkan/harvest
Click 'Run' on the sample_content harvest.
Confirm that you want to run the harvest.
Be redirected to the very ugly entity page for a harvest run entity.

Describe your changes

QA Steps

• Add manual QA steps in checklist format for a reviewer to perform. Be as specific as possible, provide examples if appropriate.

Checklist before requesting review

If any of these are left unchecked, please provide an explanation

• I have updated or added tests to cover my code
• I have updated or added documentation

[paul-m]

Oof. This is clearly wrong.