Define a new thrift endpoint for unmount with extra options

Summary:
## This Diff
Defined a new endpoint "unmountV2" which accepts UnmountArgument.

## Context
Extend eden rm with a "--no-force" flag so "--force" is not used when unmounting a mount point.

Reviewed By: genevievehelsel

Differential Revision: D69407041

fbshipit-source-id: f832db8504acf7f2b331afdb0f9dfb34c3ac9191

Author: vilatto

eden/fs/service/eden.thrift

@@ -252,6 +252,11 @@ struct MountArgument {
   3: bool readOnly;
 }
 
+struct UnmountArgument {
+  1: MountId mountId;
+  2: bool useForce = true;
+}
+
 union SHA1Result {
   1: BinaryHash sha1;
   2: EdenError error;
@@ -2020,6 +2025,7 @@ service EdenService extends fb303_core.BaseService {
   list<MountInfo> listMounts() throws (1: EdenError ex);
   void mount(1: MountArgument info) throws (1: EdenError ex);
   void unmount(1: PathString mountPoint) throws (1: EdenError ex);
+  void unmountV2(1: UnmountArgument unmountArgument) throws (1: EdenError ex);
 
   /**
    * Potentially check out the specified snapshot, reporting conflicts (and