fix(bootstrap): kubernetes 1.28 support / remove outdated feature gates

[tallaxes]

Description

Remove all feature gates passed to kubelet: CSIMigrationAzureFile, DelegateFSGroupToCSIDriver, RotateKubeletServerCertificate, fixing bootstrap on Kubernetes 1.28 nodes.

Adds 1.28 to test matrix (fixes #6), and test coverage reporting via coveralls.

Background:

DelegateFSGroupToCSIDriver feature flag is no longer supported in Kubernetes 1.28. More importantly, all of the currently set flags already default to true in all versions we care about:

Feature	Default	Stage	Since	Until
CSIMigrationAzureFile	true	Beta	1.24	1.25
CSIMigrationAzureFile	true	GA	1.26
DelegateFSGroupToCSIDriver	true	Beta	1.23	1.25
DelegateFSGroupToCSIDriver	true	GA	1.26	1.27
RotateKubeletServerCertificate	true	Beta	1.12

Reference:
https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/
https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates-removed/

How was this change tested?

• make presubmit, E2E tests, manually creating 1.28 cluster & scaling up

Does this change impact docs?

• Yes, PR includes docs updates
• Yes, issue opened: #
• No

Release Note

[tallaxes]

/test

[charliedmcb]

Overall, looks good, but a little confusing on the 1.27.x coverage, so looking for an answer there