split off webhook certs management into separate command

[OliverMKing]

Description

splits our webhook certs management code into a separate command so it can be more flexible.

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

Tested locally and unit tested

Checklist:

• [x ] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules

[coveralls]

Pull Request Test Coverage Report for Build 6832810978

• 150 of 190 (78.95%) changed or added relevant lines in 4 files are covered.
• 7 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+2.0%) to 78.99%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/webhook/webhook.go	21	23	91.3%
pkg/controller/controller.go	0	10	0.0%
pkg/webhook/cert.go	103	131	78.63%
<!--	Total:	150	190	78.95%	-->

Files with Coverage Reduction	New Missed Lines	%
pkg/webhook/webhook.go	1	86.89%
pkg/webhook/cert.go	6	75.52%
<!--	Total:	7		-->

Totals
Change from base Build 6813150888:	2.0%
Covered Lines:	2895
Relevant Lines:	3665

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💛 - Coveralls