ffac-eol-ssid: add migration for ffmuc-eol-ssid

[grische]

No description provided.

[maurerle]

On one hand, I think we should not add too many community-specific migrations to the upstream repo - on the other hand it does not hurt much and helps you to use the upstream repositories without extra hustle.
When migrations are done, we can remove the upgrade script in this package alltogether (or replace it for different communities in need).
After all, my interpretation of this repository is, to reduce the amount of time communities need to maintain and develop packages.
So I think more about the value of having everything upstream.