Forward OpenFileInAppProvider calls for OCM shares to remote reva

[ishank011]

Also closes #1032

[glpatcern]

Looks good, and I guess the gateway's Stat will take care of all that is needed (including forwarding remote errors that will be embedded in the OpenFileInAppProviderResponse).

[glpatcern]

Now this one looks good

[SamuAlfageme]

While testing this, we've seen that the 'username' encoded on the JWT token that gets forwarded to the WOPI Server (via Collabora) is the same for both the issuer and the receiver of the share:

{
   "typ":"JWT",
   "alg":"HS256"
}{
   "userid":"...",
   "filename":"/reva/daniel/test4/test.odt",
   "username":"daniel",
   "viewmode":"VIEW_MODE_READ_WRITE",
   "folderurl":"undefined",
   "exp":1599906112,
 }

Therefore, it renders the same username for both parties during a collaborative editing session. cc/ @glpatcern

[ishank011]

Can't do that with the current implementation. We're passing the same token around as the original user and can't make changes to it as we don't know the jwt secret of the other site. This won't be an issue in the public shares implementation so I think we can leave it be.