[CI] Split complexity graphs by levels

• Requested reviewers: @malenovsky @norvell @pihlajakuja @pajunen @jiaquan.huo

We had the idea internally that it would be nice to have the complexity graphs split by the proposed complexity levels to better be able to track worst case changes per level. Right now, the WMOPS line graph would be dominated by the most complex operating points always and one would not notice if e.g. the worst case of another complexity level improved or got worse. This info can be theoratically also gained from the bar graph, e.g. by adding markers denoting the levels, but due to the ordering per bandwidth and bitrate there, this would get confusing imo. An example can be found here: https://ivas-codec-pc.3gpp.org/-/ivas-codec/-/jobs/377873/artifacts/complexity-stereo-in-ext-out-public/index.html.

Please share your opinions on this.