Default ctrl plane cert expiry time to 5 years

[arkodg]

• Reverts refactor: support custom gateway cert expiry days. #2047 and instead adds a longer default of 5 years
• we should instead be recommending users to plug in their own certs docs: allow users to configure custom certs for control plane auth #866
• a backup option of overwriteControlPlaneCerts https://gateway.envoyproxy.io/latest/api/extension_types/#envoygatewaykubernetesprovider still exists
• Also fixed overwriteControlPlaneCerts yaml field name in this PR

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (397911d) 64.24% compared to head (97115f3) 64.22%.

Files	Patch %	Lines
internal/cmd/certgen.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2175      +/-   ##
==========================================
- Coverage   64.24%   64.22%   -0.03%     
==========================================
  Files         107      107              
  Lines       14922    14922              
==========================================
- Hits         9586     9583       -3     
- Misses       4762     4764       +2     
- Partials      574      575       +1     

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