Temporal sensitive test support

[big-andy-coates]

The output of some tests will depend on the current time, e.g. financial EOD processing, or weekend / public holidays, etc.

For services obtaining the current type via CreekContext#clock we can enhance the system tests to allow the clock to be adjusted to allow testing of such functionality.

A new input type should allow the test to set the clock. Additionally, chose between a test clock that is static or one that will then advance from the set point.