[pgAdmin4][Patch]: RM 4428 and 4448

Hi Hackers,

Attached is the patch to fix following issues in pgagent module:

- RM 4428 "malformed array literal error when updating pgagent job".
- RM 4448 "Error when updating connection string in pgagent Jobs."
- When user create a schedule using Create->Schedule dialog browser tree
is not showing newly created node.
- Properties tab showing same properties for all the created schedule.
- Added validation in "pga_jobstep.js", throws error on browser when we
modify step from the pgagent dialog and select the same node.

Added regression test cases to add schedule and step from the pgagent job
itself.
Please review it.

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*Thanks & Regards*
*Akshay Joshi*

*Sr. Software Architect*
*EnterpriseDB Software India Private Limited*
*Mobile: +91 976-788-8246*