Render Jira project template when searching for existing issues

[waltherlee]

#4159 enabled templating for Jira config fields project and issue_type by rendering the templates in the request body sent to create the issue:

However, it doesn't render the value in a previous request that checks if the Jira issue already exists, throwing the error:

notify retry canceled due to unrecoverable error after 1 attempts:
failed to look up existing issues: HTTP request to JIRA API: 
unexpected status code 400:
{"errorMessages":["The value '{{ .CommonLabels.project }}' does not exist for the field 'project'."],"warningMessages":[]}

This change adds the same template function to render the project value in the search request as well.

[grobinson-grafana]

There is some weird stuff happening in the tests, but it looks like they have been copied from the existing tests. We can clean those up later.

[waltherlee]

Thank you! I know what you mean: the testcase overwriting a variable used in the server handler. I copied that, but I'm working on another PR and noticed that there's another test in this file that just sets up the handler inside the testcase. I'll change it here

[grobinson-grafana]

It's fine, I would prefer if you do that in another PR actually, as I've reviewed this as is and asked for it to be merged.

[waltherlee]

Alright, will do. Thanks again

[gotjosh]

LGTM