Add member number

[reiterl]

Part of OpenSlides/OpenSlides#6759

needs the backend pr OpenSlides/openslides-backend#2412
and the meta pr in au OpenSlides/openslides-meta#99

[reiterl]

Add export of member number and update the accounts export example file.

[Elblinator]

Please add the member_number to the participant export and the example file from the participant import

in participant-import change the preview title from 'member_number' to 'Member number'

[reiterl]

Add the member number to participant export/import. You need an updated version of the backend pr to test it.

[Elblinator]

My approve was premature, please wait

[Elblinator]

Add the Member number to the account filter

[reiterl]

Waiting on the backend/meta prs to be merged.

[bastianjoel]

When creating accounts on orga level an error This member_number is forbidden is displayed.

[bastianjoel]

@Elblinator have you tested removing a member number from a user?

[Elblinator]

Removing a member number results in the same snackbar Error This member_number is forbidden

[reiterl]

Needs OpenSlides/openslides-backend#2450 to work.