[NU-1772] Refactor ScenarioActivity state handling

[mgoworko]

Describe your changes

Improvements concerning ScenarioActivity handling:

1. After discussions on Thursday we decided, that failed or in-progress activities should not be displayed (so should not be returned by endpoint). That required refactor and explicit handling of activity state. No changes in DB, only in domain.
2. Small fix - FE sends empty string as "no comment" on scenario update, fixed on BE.
3. Small fix - when scenario is modified without changing the process graph, then the activity should not contain information about scenario version. It is then correctly displayed as "Scenario updated" instead of "Version X saved".

Checklist before merge

• Related issue ID is placed at the beginning of PR title in [brackets] (can be GH issue or Nu Jira issue)
• Code is cleaned from temporary changes and commented out lines
• Parts of the code that are not easy to understand are documented in the code
• Changes are covered by automated tests
• Showcase in dev-application.conf added to demonstrate the feature
• Documentation added or updated
• Added entry in Changelog.md describing the change from the perspective of a public distribution user
• Added MigrationGuide.md entry in the appropriate subcategory if introducing a breaking change
• Verify that PR will be squashed during merge

[github-actions]

none: #7013
⚠️ Be careful! Snapshot changes are not necessarily the cause of the error. Check the logs.

[coutoPL]

LGTM