JIRA: allow different templates for jira description rendering

[valentijnscholten]

Depending on your JIRA instance or JIRA project, you may want to use different templates for rendering the issue description. Sometimes you want to provide all the details and want them to be visible in JIRA.
Sometimes you want to provide only a link back into defect dojo and not too much details.
This PR allows you to chose between these two templates, or add even more of your own templates.
Any templates added to (or modified in) dojo/templates/issue-trackers automatically become options in the jira config dropdowns.

The PR is always falling back to the default full description template already in use. So when people to do nothing after upgrading, it just keeps work as it was. It's all optional.

The PR also adds the component_name, component_version and all the SAST_xxxx fields to the "full/default" jira template, fixing #3931

BTW The first attempt at this PR was using a new model JIRAIssueTemplate that could be edited via the Django Admin portal at /admin. But this opened up risks that people could use the template language to retrieve all kinds of sensitive details. In the current world I think a lot of setups still have "everyone" as staff/superuser, so there was too much risk.
With a better permission model we could still switch to using a model instead of having to use templates on the filesystem and having to rebuild the images (or use complex mounting nobody understands ;-))

BTW2 In v2 of this PR I used the FilePathField on the model to let django populate the dropdown for us. But this resulted in the full path being stored in the issue_template field, where the template loader expects a relative path. So this required adding/removing of the prefix in some places, which broke the model validation, etc.

BTW3 So then I moved to just a CharField with choices. This worked, but if a user adds a template on disk, the choices change and django expects you to make a migration. Our initializer automatically makes those resulting in instances getting our of sync and in conflict with upstream releases.

So I fell back to just using a CharField and populating the dropdown on the forms.

[madchap]

fyi @yilmi

[madchap]

Locally tested in staging environment, works peachy :-)

This will allow us to address some teams wanting to restrict data access for confidentiality purposes, while others want all details in JIRA directly without having to navigate to Dojo.

[damiencarol]

Gave a try. it's a good feature. Maybe some users will want to add there own template in the future