impr(jira): Add new format for explicit deletes by sending diff from frontend

[Christinarlong]

Basically the flow is if we see the provider is JIRA, the feature flag ('jira-explicit-mapping-removals') is on, and the field is sync_status_forward then change the frontend mutation/payload when updating the config to be

"sync_status_forward" : {
    "123456": {"on_resolve": "123" , "on_unresolve": "456"},
    "67890":  null
     ....
}

As opposed the current of

"sync_status_forward": {
    "123456": {"on_resolve": "123" , "on_unresolve": "456"},
    "67890": {"on_resolve": "1" , "on_unresolve": "789"} 
     ....
}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[ceorourke]

lgtmy backend eyes 😵‍💫

[ceorourke]

I have a vague memory of Gabe pushing back on the naming of this "tombstone", maybe update this to whatever he suggested instead

[Christinarlong]

oop yes good catch 🙇‍♀️