Ref. Symptoms / observations / job analysis feature

Context: This step focuses on automating the process of applying symptom labels to job runs when they are finished running. This part extends previous work that identified symptoms and applied labels in ci-data-loader.
 
Action Items:

Within the job intake cloud function (ci-data-loader) when finished.json is created (prow writes this when the job is complete):

• check for label files under artifacts/job_labels (created per TRT-2465)
• if there are any, use them to create a file artifacts/job_labels/label-summary.html summarizing the labels that have been applied (based on those files) which the spyglass html lens will display. (if there's a nice way to link all the individual matches, great, but of course users can just look in the bucket files themselves.) 

Spyglass config is specified in the release repo under core-services/prow/02_config/_config.yaml - there is already a pattern under the html lens that will recognize our summary file and display it.

As much as possible, logic for writing labels (and their bucket files, and this summary file) should be located in the sippy codebase (and imported by the cloud function), to facilitate reuse by other tools doing the same things in different contexts (e.g. retroactively adding or removing labels).