Replace grass7 occurrences and update to GRASS GIS 8

[mmacata]

This is valid for multiple actinia repos and concerns. Often the actinia.cfg is affected, e.g.

grass_addon_path = /root/.grass7/addons/
grass_gis_base = /usr/local/grass7

but other parts as well. This might help: ag --ignore *json --ignore *.log* grass7

[neteler]

(kept open for https://github.com/mundialis/actinia-stac-plugin/pull/58)