Add 'Go Offline' functionality to project details page

[spwoodcock]

Is your feature request related to a problem? Please describe.

• Users will probably load FMTM in the office with internet, to get the QRCode and then download the form to ODK Collect.
• Ideally they need to prepare to going offline when out in the field.

Describe the solution you'd like

• It would be nice to have a button that is prominent on the project details page somewhere, the words 'Go Offline'.
• This should:
  • Download an existing PMTiles archive to the users browser storage (OPFS).
  • Download the data extract .flatgeobuf to the users browser storage (OPFS).
  • Allow the user to browse the map and geolocate while offline in the field.