[WOPI] Add supported view modes to app providers in /app/list

## Is your feature request related to a problem? Please describe.
In oC Web we want to support opening collaborative files in `view` (readonly) mode and then allow the user to switch to edit mode (https://github.com/owncloud/web/issues/9255).
To handle this correctly we need to know which providers support which modes for a specific mime-type.

## Describe the solution you'd like
We would like to have an additional property in the response from `/app/list`:
```json
{
"mime_type": "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
"ext": "docx",
"app_providers": [
{
"name": "Office365",
"icon": "https://res.cdn.office.net/officehub/images/content/images/favicon-8f211ea639.ico"
},
{
"name": "OnlyOffice",
"icon": "https://ocis.test/web-apps/apps/documenteditor/main/resources/img/favicon.ico"
}
],
"name": "Microsoft Word",
"description": "Microsoft Word document",
"allow_creation": true,
"default_application": "OnlyOffice"
},
```

Next to `name` and `icon` it would be great to have the available `view_modes: []` .

## Describe alternatives you've considered
Make it configurable in oC Web.
Downside: configuration split between app provider and Web, I would consider having to configure properties of app providers in web to be an anti pattern.