Allow headers on http probes

[jcmuller]

Feature Request

Use Case:

Vite dev server supports ping requests. Not on a path (why would it /s) but instead when passing in the Accept: text/x-vite-ping header.

I would much prefer to use the native http probe rather than having to use an exec one and using curl or similar.

Proposed Change:

Allow headers to be passed into the HTTP liveness and readiness probes.

Who Benefits From The Change(s)?

At least anyone who wants to use vite. There will be other cases.

Alternative Approaches

Use an exec probe with curl or similar.

[jcmuller]

If this seems like a good idea I can submit a patch for it.