POST /api/import: single step import and payload validation

[chibenwa]

Why ?

CF https://github.com/linagora/twake-calendar-frontend/issues/180#issuecomment-3371430268

We have a 2 stage import process inherited by OpenPaaS SPA.

Issues are:

• A generic file upload route looks brittle. We do not need long term storage for this
• As described in the front issue we lack validation in case the file format do not desribe an ICS

Proposal

Allow directly posting the ICS data onto POST /api/import

If Content-Type: application/json keep the existing behaviour as is for retro-compatibility.

If Content-Type: text/calendar then:

• Parse ICS data => return 400 if invalid
• Schedule an import of that data (like today)

Similar stull for Content-Type: text/vcard.

Then deprecate for removal FileUploadRoute, UploadedFileDAO and related classes