Add `overwrite` property to `toMatchSnapshot` to overwrite current snapshot

[meinaart]

Add overwrite property to toMatchSnapshot to overwrite current snapshot. Makes it easier then doing it by hand.

[ranbena]

Thisi my use case for this feature:

it('cancel button returns to original state', () => {
  // save current state
  cy.get('some-element').toMatchSnapshot({
    overwrite: true,
  });

  // do stuff
  // click cancel

  // compare to original state
  cy.get('some-element').toMatchSnapshot();
});

[kmsauter]

Implemented in commit 966dec9, you can now set the updateSnapshots flag on individual snapshots. e.g. cy.wrap(Date.now()).toMatchSnapshot({ updateSnapshots: true });