Configure the device to manually push events

[kmadisa]

TODO...

Screenshots or code snippets (if appropriate):

Definition of Done Checklist

• Code meets our python style guidelines?
• Unit tested (coded, passed, included)?
• Requested at least 2 reviewers?
• Commented code, particularly in hard-to-understand areas?
• Made corresponding changes to the documentation (e.g. Python documentation, System Engineering Documentation, version description updates, README file, etc)?

JIRA: JIRA_ISSUE_NUMBER

[kmadisa]

• Update the SimDD json schema file to include a property(ies) that signifies that the device server will push attribute events.
• Create an example SimDD json file that shows usage of the global option and overriding the global option using the attribute config property.
• Update the SimDD file parser.
• Write a simple simulator python class that extends the behaviour of the generated simulator, with command handlers that push events.
• Write a test(s) that shows that the client can receive the pushed events as specified in the SimDD.json file.