Change the default tag `job_name` to `testrun_name`

[yorugac]

Feature Description

Currently, we have two k6 tags added to all tests runs: - instance_id - an index of the k6 segment taken (1, ... n) - job_name - a Job's name which is basically a TestRun name with the same index (my-testrun-name-%d)

These two are duplicating information as they are both using the segment's index. As a consequence, both will have the same impact on cardinality of metrics.

Suggested Solution (optional)

To improve this, we could remove job_name tag and add testrun_name tag instead.

If there are drawbacks to this proposal, please let us know in the comments.

Already existing or connected issues / PRs (optional)

No response