Support the use case to trigger a flow only if some metadata has changed since the last run

[anna-geller]

Those use cases might be possible by combining trigger conditions with the KV store (to not evaluate the trigger conditions to true i.e. to fire new execution if some data didn't change as compared to the last timestamp in KV store) -- not sure if feasible, may be sth we can leverage real-time trigger's statefulness for

• start a flow only if new data is ingested
• start a flow only if some data has been deleted