[stable/vpa] securityContext on admission controller certgen

[adavid44]

Why This PR? Handle securityContext on certgen pod

Fixes #

Changes Changes proposed in this pull request:

• Add the admissionController.certGen.securityContext block for certgen pod

Checklist:

• [x] I have included the name of the chart in the title of this PR in square brackets i.e. [stable/goldilocks].
• [x] I have updated the chart version in Chart.yaml following Semantic Versioning.
• [x] Any new values are backwards compatible and/or have sensible default.
• [x] Any new values have been added to the README for the Chart, or helm-docs --sort-values-order=file has been run for the charts that support it.

[CLAassistant]

All committers have signed the CLA.

[nerzhul]

We'd like to have this PR too as we don't permit to run with no security context on our side :)

[adavid44]

Hello :wave: Any update on this MR ?