[Security Solution] [Threat Hunting] [Cases] Allow User to Specify Atlassian Jira Ticket fields from Cases UI

[shimonmodi]

Describe the feature:
Our current case capability allows users to send a case to external systems like ServiceNow ITSM, Atlassian Jira and IBM Resilient. This feature will allow users to specify case specific data that needs to be sent over to the external system (as described by their data model).

Describe a specific use case for the feature:
Elastic's case feature supports analyst workflow for collecting various pieces of evidence that are relevant to an investigation, and as a collaboration feature that lets other analysts view the existing details and comment on it. Jira offers a lot of flexibility to end users when they natively create an issue/ticket in Jira. We need to provide a way for users to be able to fill out thos Jira fields from our cases interface. When an analyst is ready to push a case to an external systems configured as a connector, they will be provided issue/ticket fields that are populated from Atlassian Jira data model.

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)

[cnasikas]

#73778: Connector & Alerts

[cnasikas]

#77327 add support for issue type, priority, and parent in the case of a subtask.