Give app developer the option to change texts on the "you can't start this app" page

[SandGrainOne]

Description

The page displaying validation messages from the InstantiationHandler.RunInstantiationValidation() method in an app currently only display standard texts in addition to the generated messages.

The page must support all text resource features like language, variables and markdown. It should be possible to replace the standard texts with custom texts and it should be possible for the method to return text resource keys. (This last bit might already be supported, must be tested/verified.)

It could also be that the page needs a design refresh. See screenshot.

⚠️ NOTES ⚠️ This issue is implicitly solved by introducing the new texts microservice.

Screenshots

The current version of the page as of the creation of this issue.

Considerations

Ops requirements

Acceptance criteria

Specification tasks

• [ ] Development tasks are defined

Development tasks

Test

Definition of done

• [ ] Documentation (docs.altinn.studio) is updated (if relevant)
  • [ ] Technical documentation
  • [ ] User documentation
• [ ] QA
• [ ] Manual test is complete (if relevant)
• [ ] Automated test is implemented (if relevant)
• [ ] All tasks in this userstory are closed (i.e. remaining tasks are moved to other user stories or marked obsolete)