Add --request-timeout CLI flag to customize k8s api client timeout

[mgerasimchuk]

These changes fix the #179 issue by adding --request-timeout CLI flag

Example of usage ksnif after merging these changes:

kubectl sniff --request-timeout 520s --pod-creation-timeout 520s -p -n default nginx-69f9fb6f84

[mgerasimchuk]

Hi @bostrt,

Could you have a look?

PS:
I build it and tested it in the real case, new flag works and solved my issue.