Replace or fix `warp` in `admission_controller` example

[clux]

warp no longer comes with tls stuff since seanmonstar/warp#1121
turned off dependabot for it: #1802

leaving an issue here to remind us to do one of:

• upgrade when/if it gets support back
• manually do tls in there
• move it to axum for the example, as it has more traction/updates generally.

in either case let's wait a bit and see. axum 0.9 is in progress with breaking changes, and warp 0.4 just dropped.