Support proxy_url

[mathe-matician]

The original repo's master had changes to support proxy_url: https://github.com/gavinbunney/terraform-provider-kubectl/blob/8e4af599e17a3d8d73defd5cff392bbe23cc9c6f/kubernetes/provider.go#L124-L129

Since this is the now active repo, it would be great to implement support for proxy_url here.

[thpham]

Would be very cool to move forward with that. @alekc , If I take some time to propose a PR, would you be ok to review, merge and do a new release ?

[alekc]

released in https://github.com/alekc/terraform-provider-kubectl/releases/tag/v2.0.4-rc1 (rc version, so you need to set explicit versioning in your tf file). @mathe-matician @thpham

[alekc]

Also, since you've required this functionality please confirm that it's working properly. I am a bit limited in testing it due to the nature of the requirement (don't have a proper proxy with certs or socks set up).

[thpham]

This looks ok for me for now, because I never had the chance to test the original feature as it was in the main branch but not in the last release. But I will probably be able to test again over Xmas time.

[alekc]

Released in 2.0.4