How to set the body limit for HTTP requests

[hannahbast]

As reported in #1088, for very large requests (e.g., due to a very large VALUES clause), the server currently does not provide a response. In the QLever log, the following error message appears, which originates from a call to boost::beast::http::async_read:

ERROR: body limit exceeded: body limit exceeded

This PR works around this limitation by setting the body limit explicitly in the code. The body limit could easily be made into a command line argument.

Here is a generic query to test whether it works for large requests (with the current master, this request shows the behavior explained above, with this PR it works fine):

N=100000; curl -s http://localhost:7015 -H "Accept: text/tab-separated-values" -H "Content-type: application/sparql-query" --data-binary @<(echo "SELECT * WHERE { VALUES ?x { $(seq 1 $N | tr '\n' ' ')} }")

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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