Match tag styles on meeting and orga level

[Elblinator]

for reference see OpenSlides/openslides-client#3595

The Tags on the meeting level need a new field and actions

• they need the additional colour field

• and the ability to set it using tag.update and -create

• for already created tags I would recommend setting the colour to the accent colour

[luisa-beerboom]

This would cause the meeting tags to be functionally the exact same as the organization tags with the exception of the owner id field (i.e. meeting_id/organization_id).
Given that this requires a migration anyway, we could think about unifying the models