1.38.0

Various fixes & improvements

• Only add trace context to checkins and do not run event_processors for checkins (#2536) by @antonpirker
• Metric span summaries (#2522) by @mitsuhiko
• Add source context to code locations (#2539) by @jan-auer
• Use in-app filepath instead of absolute path (#2541) by @antonpirker
• Switch to jinja2 for generating CI yamls (#2534) by @sentrivana