Add optional branch_name_include_substring parameter to snapshot_get_branches,
if provided only branches whose name contains the given substring will be
returned.
Add optional branch_name_exclude_prefix parameter to snapshot_get_branches,
if provided branches whose name starts with the given pprefix will not be
returned.
The purpose is to add branches filtering in swh-web. As that feature
could be useful elsewhere, I thought adding it at swh-storage level
was better than implementing it client side each time it is required.
Related to T2782