Tweak the Nuxeo instance to handle more connections

Have tests running in parallel breaks the basic Nuxeo instance used via maven (here with 4 users at the same time):

HTTPError(500), error: Connection pool is fully used, consider increasing nuxeo.vcs.blocking-timeout-millis (currently 100) or nuxeo.vcs.max-pool-size (currently 20), server trace: None

Given some documentation, we should tweak the server configuration to be able to handle more connections:

• https://doc.nuxeo.com/nxdoc/repository-configuration/
• https://doc.nuxeo.com/nxdoc/managing-performance/#connection-pools
• https://doc.nuxeo.com/nxdoc/managing-performance/#common-problems-andamp-hints