Consolidate all services to use the Reva config struct for the shared package.
This works because all services (except 'notifications', 'thumbnails' and
'webdav') where using the same config keys and environment variables for
setting the reva gateway.
We now default LDAP_GROUP_SUBSTRING_FILTER_TYPE and LDAP_USER_SUBSTRING_FILTER_TYPE
to "any", which means full substring search. The previous default was just using prefix
matching.
Closes#4282
This introduces new settings for the users and groups services.
"group_substring_filter_type" for the group services and
"user_substring_filter_type" for the users service. They allow to set
the type of LDAP filter that is used for substring user searches.
Possible values are: "initial", "final" and "any" to do either prefix,
suffix or full substring searches.
Fixes#547
The help flag is configured automatically by default already. We don't
need to redo that for every single service.
This also addresses one of the finding of "go race" (#4088)
