stripping of query whitespace on [POST] with `application/sparql-update`

[MikiDi]

SPARQL Update queries through [POST] with Content-Type: application/sparql-update aren't stripped from their whitespace.

curl -v --http1.1 -X POST \
  http://localhost:8892/sparql \
  -H "Content-Type: application/sparql-update" \
  --data-binary ' INSERT DATA { <http://ext.com/gv> <http://ext.com/pp> "value" }'

(notice the blank space before insert data)

{"status":500,"message":"Failed to process query.","mu-call-id":[],"mu-call-id-trail":[],"mu-session-id":[],"mu-auth-sudo":[],"mu-auth-allowed-groups":"[]","mu-call-scope":"_","internal-error":"No matching token found at position 0\nValid options: (\"ADD\" \"BASE\" \"CLEAR\" \"COPY\" \"CREATE\" \"DELETE\" \"DELETE DATA\" \"DELETE WHERE\" \"DROP\" \"INSERT\" \"INSERT DATA\" \"LOAD\" \"MOVE\" \"PREFIX\" \"WITH\")\nStack top: UpdateUnit","source-ip":"172.25.9.1"}

cc @nbittich