Bug 24775: Add ID to POS submit payment button

Bug 24775: Add ID to POS submit payment button

This patch simply adds an ID to the submit button to make it easier to
overide styling and functionality.

Test Plan:
0/ Inspect the element on page and note there is no id
1/ Apply patch
2/ Refresh page
3/ Inspect the element on page and note there is now an id

Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>