Refactor and UI-polish around activity calendar on user profile

What does this MR do?

Refactors and UI-polishes the activity calendar on user profile.

• UX Fixes the height of the element of the activity calendar to avoid re-rendering on SVG rendering.
• UX Removes ugly UX on failure of the activity calendar on user profile.
• UX Even on failure, a viewer (user) can easily retry to partially reload the calendar without reloading the whole page of the user profile.
• ~"technical debt" Removes unused CSS and classnames.

Screenshots (strongly suggested)

Before (still)	After (24s movie)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• [n/a] Merge request performance guidelines
• Style guides
• [n/a] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #283924 (closed)