add option for mpi kubectl delivery

[zw0610]

What this PR does / why we need it:

In mpi-operator, user can specify which kubectl-delivery image to use in launch argument. Such feature is missing in training-operator. This pr follows the pytorch init container image option style and adds mpi-kubectl-delivery-image to launch options.

Which issue(s) this PR fixes (optional, in Fixes #<issue number>, #<issue number>, ... format, will close the issue(s) when PR gets merged):
Fixes #

Checklist:

[coveralls]

Pull Request Test Coverage Report for Build 1721937590

• 97 of 124 (78.23%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 36.742%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/controller.v1/mpi/mpijob_controller.go	97	124	78.23%

Files with Coverage Reduction	New Missed Lines	%
pkg/controller.v1/mpi/mpijob_controller.go	1	75.16%

Totals
Change from base Build 1703226821:	-0.03%
Covered Lines:	2267
Relevant Lines:	6170

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💛 - Coveralls

[terrytangyuan]

Thanks!

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: terrytangyuan, zw0610

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