kube-runtime: make ExponentialBackoff public

[gdeleon2]

Change ExponentialBackoff to public so that it is accessible for external use.

[clux]

the interface is not really ready to expose as is, but i am open to some alternatives here.

maybe we can impl Default for ExponentialBackoff and maybe rename it to KubernetesBackoff or something to indicate it's an upstream convention.

if you do actually need to set the parameters, then maybe we can make the fields of that struct pub.

could you tell us a little bit about the use case for needing to instantiate this yourself?

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 76.1%. Comparing base (55e865c) to head (a62f925).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
kube-runtime/src/watcher.rs	0.0%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1716     +/-   ##
=======================================
- Coverage   76.1%   76.1%   -0.0%     
=======================================
  Files         84      84             
  Lines       7858    7860      +2     
=======================================
  Hits        5977    5977             
- Misses      1881    1883      +2     

Files with missing lines	Coverage Δ
kube-runtime/src/watcher.rs	42.8% <0.0%> (-0.3%)	⬇️

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[clux]

LGTM. Thanks!