dynamic jobProvider and suggestionComposer registration

[sperlingxx]

Add registry for jobProvider and suggestionComposer, so it is easy to add new Provider or Composer via init function without modifying existing files.
In addition, Provider includes an additonal method MutateJob, which allows some custom mutation on jobSpec before its creation.

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This change is 

[k8s-ci-robot]

Hi @sperlingxx. Thanks for your PR.

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[gaocegege]

Thanks for the PR. Generally LGTM with some nits

[andreyvelich]

/ok-to-test

[sperlingxx]

@andreyvelich I think this PR is ready.

[andreyvelich]

/retest

[andreyvelich]

@sperlingxx Thanks!
/lgtm
/cc @gaocegege

[gaocegege]

/approve

Thanks for the PR!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gaocegege

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[johnugeorge]

/retest