deprecate LASH support

[theGreatWhiteShark]

After introducing myself into LASH in the context of #1645 I found neither LASH nor LADISH being included in most Linux distributions anymore. Also LASH seems to be unmaintained while Linux audio community has focused on NSM - which we already support - and build a large ecosystem around it. There are even plans for LADISH to support NSM as well in future releases (see discussion of linked PR).

Since LASH requires a number of ifdefs in our code we can not in our test pipeline (since there is no LASH support), we suffer bit rot (e.g. #2076).

LASH will be marked deprecated in 1.2.5, and removed it in 2.0.