Add links to Jira-related error messages

What does this MR do and why?

Related to #337996 (closed), following on from !66987 (comment 644747021).

When we say...	We link to...
Jira integration configuration	https://docs.gitlab.com/ee/integration/jira/configure.html
Jira integration credentials	https://docs.gitlab.com/ee/integration/jira/#authentication-in-jira

Screenshots or screen recordings

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.