Optional `update_job` callback in `Quantum.Storage`

[pnezis]

Add an optional update_job callback in Quantum.Storage. If this is implemented then it will be called when a job gets updated, otherwise the previous behaviour (delete and then add the job) will be used.

Rationale: I have created a postgres storage and the jobs are linked to other tables through foreign keys. With the current implementation every time a job is updated it deletes the current job and adds it again. I want to be able to just update the properties that have changed and leave everything else untouched.

[maennchen]

Thanks a lot. ❤️ I'll merge when the CI passed.

[coveralls]

Pull Request Test Coverage Report for Build 46a44c435babfa68866a30eae98989dc53cab0a4-PR-467

• 10 of 10 (100.0%) changed or added relevant lines in 2 files are covered.
• 28 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-8.02%) to 78.83%

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Files with Coverage Reduction	New Missed Lines	%
lib/quantum/date_library.ex	1	55.0%
test/support/test_storage.ex	1	89.47%
lib/quantum/executor.ex	2	90.91%
lib/quantum/execution_broadcaster.ex	24	41.38%
<!--	Total:	28		-->

Totals
Change from base Build 02e519fe0710b7c64a34762e3d3034d3ffb61aef:	-8.02%
Covered Lines:	283
Relevant Lines:	359

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💛 - Coveralls

[pnezis]

@maennchen Please have a look at the tests issue I opened. I had to disable the tests locally in order to properly test the changes.

[maennchen]

@pnezis Do you have time to have a look by yourself and open a PR as well? I don't have time at the moment and it may take some time until I can look at it.

[pnezis]

@maennchen Here you are #468

[rogeriochaves]

hey @pnezis, could you share your postgres storage implementation?