Add ability to change own structure level in a LoS

[Elblinator]

Current behaviour:
(connected Issue #3336 )
If a participant is not allowed to manage a LoS then they cannot change their own structure level

Reproduction:

1. project something onto the autopilot
2. navigate to this LoS
3. make sure that the deligates group can see other participants on the LoS, but not manage the LoS
4. connect structure level with countdown
5. put user A (with one structure level) on the LoS
6. as admin you can change teh structure level from A
7. login as User A
8. Navigate to the LoS
9. you cannot change your own structure level

Wanted behaviour:
A participant should be able to change their own structure level (same as to how they are allowed to add/remove Pro/Conta)

[Elblinator]

closed due to merged PR