Set overrides in DSS as a single property, refactor code for submitting runs

[eamansour]

Why?

See galasa-dev/projectmanagement#2000

Changes

• Instead of setting multiple dss.framework.run.X.override.<override-property> properties into the DSS, the framework will now only set a single dss.framework.run.X.overrides property containing multiple overrides in a JSON array, for example:

dss.framework.run.C123.overrides=[{"key": "my.first.override", "value": "abc"}, {"key": "my.second.override", "value": "123"}]

• Updated the consuming code in the test runner and framework initialisation to pull overrides out of this new property
• Refactored the submitRuns method in the FrameworkRuns class and added unit tests

[techcobweb]

Looks good, if you can address my few comments pls.