Add partial support for DownwardsAPI with kctrl package release

[100mik]

What this PR does / why we need it:

This PR allows Packages using DownwardsAPI to obtain kubernetesAPIs or kubernetesVersion by feeding a false value. However this value cannot be reliably used to introduce images in the template step for the time being. This does not block users who are not conditionally introducing images based on these parameters. It mocks CoreV1 client calls made by GetServiceAccountToken

Which issue(s) this PR fixes:

Partially fixes #1523

Does this PR introduce a user-facing change?

Additional Notes for your reviewer:

Review Checklist:

• [x] Follows the developer guidelines
• [x] Relevant tests are added or updated
• [x] Relevant docs in this repo added or updated
• [x] Relevant carvel.dev docs added or updated in a separate PR and there's a link to that PR
• [x] Code is at least as readable and maintainable as it was before this change

Additional documentation e.g., Proposal, usage docs, etc.:

We should document that using `kappControllerVersion` with DownwardAPI can lead to failures while releasing packages