Adds header-actions slot to uui-box

[nathanwoulfe]

Description

To allow additional controls in the box header, I've added a new slot, header-actions which renders on the right side of the header. This is something I needed for Workflow, but will also be used for the rollback/history panel on Document Info.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (minor updates related to the tooling or maintenance of the repository, does not impact compiled assets)

Screenshots (if appropriate)

[github-actions]

Azure Static Web Apps: Your stage site is ready! Visit it here: https://delightful-beach-055ecb503-676.westeurope.azurestaticapps.net

[github-actions]

Azure Static Web Apps: Your stage site is ready! Visit it here: https://delightful-beach-055ecb503-676.westeurope.azurestaticapps.net

[github-actions]

Azure Static Web Apps: Your stage site is ready! Visit it here: https://delightful-beach-055ecb503-676.westeurope.azurestaticapps.net

[github-actions]

Azure Static Web Apps: Your stage site is ready! Visit it here: https://delightful-beach-055ecb503-676.westeurope.azurestaticapps.net

[nielslyngsoe]

I did refactor slightly to get rid of the 'header-left' element. As that was not stricly necessary :-)

Very well done with tests and description corections and story updates!!

[bjarnef]

@nielslyngsoe just though if actions is the best wording? Could it be used for something that isn't an action like a notice or info?
Maybe header-extra / header-extras ?

[bjarnef]

It seems this affected a bit packages which used headline slot. Even though header-actions isn't used, it seems to take up take space.
ByteCrumb/Umbraco.Community.DeliveryApiExtensions#32