net/k6: Update to 0.28.0

Changelog[1]:

• Cloud execution logs
• Pushing k6 logs to loki
• Optional port to host mappings
• Support for specifying data types to InfluxDB fields
• Support for automatic gzip-ing of the CSV output result
• Various enhancements in UX
• Several bugfixes

[1] https://github.com/loadimpact/k6/releases/v0.28.0

PR: 250095
Submitted by: Lewis Cook <vulcan@wired.sh> (maintainer)
Approved by: arrowd (mentor)
Differential Revision: https://reviews.freebsd.org/D26673