fix(files): page h1 heading

[ShGKme]

Summary

• A regression from fix(files): combine navigation and files list into single Vue app #43090
• In the past heading was set via DOM API in

  server/apps/files/src/views/Navigation.vue

  Line 190 in bb87232

  setPageHeading(view.name)

• This doesn't work on Full Vue app. After migrating to NcContent, it has to be set here via page-heading prop
• The same heading is used, but with "Files" as a fallback

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[ShGKme]

/backport f12d36b to stable28