Added a new OpenInApp request/response

[glpatcern]

This will eventually supersede OpenFileInAppProvider.

The rationale being that OpenInApp generically refers to refs, i.e. files AND directories, and a new optional parameter app was added, to allow:

1. In case of folders, to specify the app as the default logic to map mimetypes to apps cannot apply
2. In case of files, to allow overriding the default logic and support the case where the user asks to "Open with..." and multiple applications are registered for the same mimetype (typical case: .docx -> MS Office Online, OnlyOffice, Collabora Online).

[SamuAlfageme]

LGTM! All in for this open request version in steroids! 🙌

[ishank011]

Maybe just add the optional app field to the current request? If it's empty, do what you're doing now, else the changed implementation

[glpatcern]

Maybe just add the optional app field to the current request? If it's empty, do what you're doing now, else the changed implementation

Not sure I understand - this is precisely what this PR is doing. Or do you mean to modify also the OpenFileInAppProvider request? But the idea is to deprecate it - essentially have it renamed to OpenInApp, without references to File.