Create a entry in the system note history to indicate what information was exported to SCKAN

User Story: We would like the ability to know exactly what a population looked like at a given time when exported for feeding SCKAN. This can help us create a version history of the population over time. This extends the current notation that states who transitioned the statement to exported. We want 2 functions: 1 - provide the statement preview. 2 - compare this statement preview to the last statement preview recorded. Is this a new statement (never exported before) or updated statement or unchanged statement.

Acceptance Criteria:

- create a system note when a statement is transitioned from npo approved to exported,
"The exported statement has the following statement preview: [statement preview]"
- create a system note when a statement preview is different than the previous statement preview, "The statement has been updated since the last export"
- create 2 new metrics in the Export Batch and Metrics page in the admin area
- New connectivity statements: [helper text reads: Number of new connectivity statements exported in this export batch]
- Updated Connectivity statements: [helper text reads: Number of updated connectivity statements exported in this export batch]
- Place the new and updated connectivity statements below the Connectivity statements section here: