Automatic merge from submit-queue (batch tested with PRs 50023, 50639)

Correct case for starting character of option string

**What this PR does / why we need it**:

Kubectl-conventions.md states:

   "Flag descriptions should start with an uppercase letter and not have a period at the end of a sentence"

There are numerous cases where this is violated in `kubectl/cmd`. This PR is the result of an audit of all source files under `kublet/cmd` and corrects the case of the initial Flag description character.

/sig cli
/kind cleanup
/kind documentation

**Release note**:
```release-note
NONE
```