Use NLB as default SLB provider

[xuanyunhui]

What would you like to be added:

Use NLB as default SLB provider

Why is this needed:

CLB is old SLB product in Alicloud， Instead NLB for layer 4 and ALB for layer 7 is better，so I think make NLB is default for layer 4 load-balancing is good choice.

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/lifecycle stale