Enable support for 'major incidents' in JIRA

[FernandesMF]

Freshmaker currently supports major incidents only in Bugzilla, but some products file those trackers in JIRA.

This commit implements the logic to check if a tracker in JIRA corresponds to a major incident, by using the Errata API.

The changes are the following:

• new function Errata.has_jira_major_incidents to check if a tracker in JIRA refers to a major incident
• new function Errata._get_jira_issues to fetch jira trackers
• inclusion of the new check in ErrataAdvisory.from_advisory_id, to add support to the JIRA trackers
• renaming of 'hightouch' to 'major_incident' in several points across the codebase, to reflect the new logic
• a new unit test for Errata.has_jira_major_incidents, with all the expected cases that it should handle
• adjustment to tests and configuration values, to conform to the new logic

JIRA: CWFHEALTH-2360