Expose FS type information per storage

To better understand what storage types are in production, Gitaly should
expose the type of filesystem. The return value is a string, not the raw
value, so Gitaly needs to map these.
4 jobs for zj-fs-type in 1 minute and 36 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Test
passed #216364246
build

00:01:27

passed #216364247
check-grpc-proto-clients

00:01:36

passed #216364248
danger-review

00:01:33

passed #216364244
test

00:01:27