Implement custom events suggestions

[zoldar]

Changes

Depends on #4033

Add support for suggesting events when defining custom goal events.

TODO

• [ ] fix modal not resetting combobox state when it should

Tests

• [ ] Automated tests have been added
• [ ] This PR does not require tests

Changelog

• [ ] Entry has been added to changelog
• [ ] This PR does not make a user-facing change

Documentation

• [ ] Docs have been updated
• [ ] This change does not need a documentation update

Dark mode

• [ ] The UI has been tested both in dark and light mode
• [ ] This PR does not change the UI