Add startup probes validation for user and sidecar containers

[flomedja]

/area API
/kind good-first-issue

Describe the feature

While working on the #15823 I noticed that we don't do the validation of the StartUp probes defines in the user and sidecar containers.
It might be useful to add validation as it is done for the readiness and liveness probes

[mienpham04]

Hi @flomedja, can you assign me to work on this issue?

[flomedja]

@mienpham04 I don't have the rights to assign someone on an issue. @dprotaso @skonto Can you help with this ?

[linkvt]

You can use the /assign command in a separate line to assign the ticket to yourself.

I'll assign you directly
/assign @mienpham04