[MM-21762] Refactor jira issue search

[mickmister]

Summary

This PR refactors the issue search endpoint to be more flexible, so the epic search can use the same endpoint. This is useful to allow for more help wanted tickets centered around searching for issues.

Ticket Link

https://mattermost.atlassian.net/browse/MM-21762

[cpoile]

Very nice, thanks @mickmister !

[levb]

Nice!!!

[levb]

@DHaussermann ready for you to regression-test

[DHaussermann]

@mickmister there seems to be an issue with this change. For the "Attach to Jira" functionality, searching when the search terms includes spaces no longer seems to return correct results.
For example, if the title dkh filter test 10 exists I see the record included when searching for "dkh" but when I type "dkh filter" to refine my search I see no results.

This appears to be a regression from the behavior on master. I tested with the same data-set.
Searching with spaces on subscription filters appears to behave normally.

[mickmister]

@DHaussermann Found the issue. I was encoding the user's string, as well as the query string itself, resulting in double encoding. Your test case works correctly now.

[cpoile]

Nice catch @DHaussermann !

[DHaussermann]

Tested and passed
Issue search is now working as expected

• Single word
• Multiple word
• Matches when words are out of order
• Partial matches when numbers are strings "1" matches "1", "10", "12"
• Issue keys can be searched
• Searches summary and description of issues
• etc...
  Also looked at Epic search again quickly
  LGTM!