ec: dynamically discover disk types from topology for evacuation

Disk types are free-form tags (e.g., 'ssd', 'nvme', 'archive') that come
from the topology, not a hardcoded set. Only 'hdd' (or empty) is the
default disk type.

Use collectVolumeDiskTypes() to discover all disk types present in the
cluster topology instead of hardcoding [HardDriveType, SsdType].

test/erasure_coding/ec_integration_test.go

@@ -1282,7 +1282,7 @@ func TestECDiskTypeSupport(t *testing.T) {
 		args := []string{
 			"-collection", "ssd_test",
 			"-sourceDiskType", "ssd", // Filter source volumes by SSD
-			"-diskType", "ssd",       // Place EC shards on SSD
+			"-diskType", "ssd", // Place EC shards on SSD
 			"-force",
 		}