Updated the description of k6 Prometheus (remote write)

[sjyothi54]

Ticket: https://new-relic.atlassian.net/browse/NR-232582
Description: Spotted description for k6 Prometheus (remote write) extends beyond the confines of the description box.
Attaching the screenshot of documentation description

Pre merge checklist

• Did you check you NRQL syntax? - Does it work?
• Did you include a Data source and Documentation reference?
• Are all documentation links publicly accessible?
• Did you check your descriptive content for voice and tone?
• Did you check your descriptive content for spelling and grammar errors?
• Did you review your content with a subject matter expert? (e.g. a Browser agent quickstart is reviewed with a member of the Browser Agent team)

Dashboards

• Does the PR contain a screenshot for each of your dashboards?
• Do your screenshots show data?
• Has the sanitization script been run on each dashboard?

Alerts

• Did you check that your alerts actually work?

[RamanaReddy8801]

LGTM!