Integrate REVA appprovider

[wkloucek]

oCIS WOPI server duplicates code which is already in REVA. This can be used with the OpenInApp request like done in owncloud/ocis-wopiserver#16.

In order to use the OpeninApp request we need to integrate / start the AppProvider in oCIS like done in #2204.

Also a rework of the AppProvider and the CS3 WOPI server are in progress:

• https://github.com/cs3org/wopiserver/blob/master/CHANGELOG.md#tue-jun-29-2021---v700
• Extend app registry with AddProvider method and mimetype filters cs3org/reva#1785, Revamp Application Registry cs3org/reva#1779

further TODOs:

• see requirements for integration into ownCloud Web
• Extend oCIS extensions for native clients (desktop and mobile) #59

[wkloucek]

futher procedure:

• merge Use a URL object in OpenInAppResponse cs3org/reva#1968
• update REVA in oCIS
• merge add app provider and app provider registry #2204

-> /app/list/ and /app/open/ endpoints are available in oCIS

• wait for mimetype handler / extension bootstrap overhaul in oC Web let extensions register more flexible file open actions web#5135

-> write small app provider app for ownCloud Web, that uses /app/list/ endpoint for registering file handlers and does the file handling action (do /app/open request and then open in iframe)

cc @fschade

[wkloucek]

Integration work in oC Web is also in progress:

• Introduce Skeleton-Application, Runtime hooks and demystify runtime boot logic  web#5752
• App Provider web#5712

[wkloucek]

Current state:

• Fix needed fix app open when multiple app providers are present cs3org/reva#2118
• Add file actions in oC Web [full-ci] Internalize app provider web#5805

Missing in general:

• documentation
• archive oCIS WOPI server
• update deployment example add OnlyOffice and CodiMD to wopi deployment example #2478

Missing in oC Web:

• default action
• new file dialog
• Fix Context menu items at the extreme ends are inaccessible web#5845