Remove rand dependency in favor of tungstenite fn

[clux]

Found tungstenite::handshake::client::generate_key which is blanket re-exported via tokio-tungstenite (which we already depend on under ws feature)

we still use rand as a dev dependency, but less explicit things on users, and less re-implementing the same logic.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.8%. Comparing base (267c224) to head (a35dcc8).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1691     +/-   ##
=======================================
- Coverage   75.8%   75.8%   -0.0%     
=======================================
  Files         84      84             
  Lines       7629    7626      -3     
=======================================
- Hits        5779    5776      -3     
  Misses      1850    1850             

Files with missing lines	Coverage Δ
kube-client/src/client/mod.rs	75.8% <100.0%> (ø)
kube-client/src/client/upgrade.rs	75.0% <ø> (-3.2%)	⬇️