Adapt directory loader visit type depending on the vcs tree to ingest

Prior to this, it was sending only 'directory' types. Multiple directory loaders now exist whose visit type are currently diverging, so the scheduling would not happen correctly without it. See [1] [2] [3]. This is the required commit adaptation for the scheduling to work appropriately.

[1] swh-loader-svn!221 (merged): Add SvnDirectoryLoader

[2] swh-loader-git!154 (merged): Add GitDirectoryLoader

[3] swh-loader-mercurial!130 (merged): Add HgDirectoryLoader

Refs. swh/meta#4979 (closed)