[Cases] Bidirectional sync for case connectors

[shanisagiv1]

Describe the feature:
In order to support a better incident closure. we need to provide a bidirectional sync between our case and the ticket in the target system.
To allow that we need to improve our connector framework and adjust each connector to map between the target system and the case fields.

The bidirectional sync means that once the ticket is opened in the target system each of the defined fields will be synced back to the case when it changes.

• Status
• Tags
• Severity
• Comment
• Ticket URL
• Dedicated fields depends on the connector.
• Custom fields - see Allow users to define custom fields on Kibana cases #155380
• Linked Artifacts - links to ML jobs, timelines, etc.

Describe a specific use case for the feature:

• The user is able to define what connector type should be triggered when a case is created ( this is out of scope for this ticket since it changes the way case connectors work today. Currently it's manual push only with one-way sync - [TBD - ticket for automatic case connector])

• The user is able to map between the target system fields and the case fields. This should be done in the 3rd party app/config panel. The mapping should support fields (ootb and custom fields) and value mapping for example:
  issue severity (in target) --> severity (in case)
  P1 --> Critical
  P2 --> High
  etc.

• On each update, the last sync is updated on the case.

• when a comment is synced, the connector should add an annotation that says that it was added by the target sys

Notes:

• Soon we'll support Split/merge options on cases, this should be taken into consideration when planning the bi-di sync. probably the sync will remain effective just to the original case when splitting and stop syncing when merging - this can be decided later on but important to keep in mind.

Competitors with Bidi sync to Snow:

• https://kb.victorops.com/knowledge-base/servicenow-bi-directional-integration-guide/
• https://techcommunity.microsoft.com/t5/microsoft-sentinel-blog/microsoft-sentinel-incident-bi-directional-sync-with-servicenow/ba-p/1667771

Similarly, we should be able to support BiDi sync from alert level to 3rd parties - TBD ticket link

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