chore: allow text/plain contentType for rest request's body types

[NagyZoltanPeter]

Background

@weboko
"nwaku does not allow cross origin requests explicitly.
Because of that browser should send request with no-cors mode which downgrades request to Content-Type = text/plain;charset=UTF-8
nwaku of course rejects with it making it impossible to interact "

Details

Normally nwaku rest interface expect application/json content types but nothing prevent to attempt interpret plain text body types convert as from json format. Of course if something will not match we need to return specific error.

Acceptance criteria

• all previous functionality must keep working, but rest request with text/plain contentType descriptor must be accepted either.

[NagyZoltanPeter]

Weekly Update

achieved:
next: Allow text/plain contentType on RestApi is on PR, libwaku Fedora build issue

[NagyZoltanPeter]

Weekly Update

achieved: Better support for js-waku using RestApi: Allow text/plain contentType
next: Bandwidth management preparation