Embed observability

What does this MR do and why?

gitlab-org/opstrace/opstrace-ui#124 (closed)

Recognises when an observability url, beginning with https://observe.gitlab.com/, is pasted into the description or content editor of an Epic/Issue/MR and places an iframe with the same source as the pasted url.

• This issue, under this epic

Screenshots or screen recordings

How to set up and validate locally

Setup instructions

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.