feat: support kubelet server certificate rotation

[cameronmeissner]

What type of PR is this?

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Special notes for your reviewer:

Release note:

none

[coveralls]

Pull Request Test Coverage Report for Build 9617595817

Details

• 23 of 27 (85.19%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 76.026%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/agent/utils.go	18	22	81.82%

Totals
Change from base Build 9610979529:	0.06%
Covered Lines:	2648
Relevant Lines:	3483

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9650980015

Details

• 23 of 27 (85.19%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 76.026%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/agent/utils.go	18	22	81.82%

Totals
Change from base Build 9638714944:	0.06%
Covered Lines:	2648
Relevant Lines:	3483

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9651029644

Details

• 25 of 31 (80.65%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 75.997%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/agent/utils.go	20	26	76.92%

Totals
Change from base Build 9638714944:	0.03%
Covered Lines:	2650
Relevant Lines:	3487

---

💛 - Coveralls