Increase web project merge request TTFB

Increase k6/tests/web/web_project_merge_request.js TTFB a bit to reduce the intermittent failure like https://gitlab.com/gitlab-org/quality/performance/-/jobs/2098467867

Additionally adding result to InfluxDB reporting - would like to explore adding a graph for results, as for Web tests with multiple endpoints TTFB graph can show successful threshold however the test itself fails like with web_project_merge_request example above.