Change TrimLeft for TrimPrefix on the from-to-www redirect

[snelis]

What this PR does / why we need it:
This is a fix for the redirect from to www functionality in combination with a domain that starts with a w
Right now it uses a TrimLeft which means www.we-foo-bar.com becomes e-foo-bar.com.
I think a better solution would be to use TrimPrefix

[codecov-io]

Codecov Report

Merging #2477 into master will decrease coverage by 0.05%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #2477      +/-   ##
==========================================
- Coverage   41.67%   41.61%   -0.06%     
==========================================
  Files          74       74              
  Lines        5291     5291              
==========================================
- Hits         2205     2202       -3     
- Misses       2790     2792       +2     
- Partials      296      297       +1

Impacted Files	Coverage Δ
internal/ingress/controller/nginx.go	11.26% <0%> (ø)	⬆️
cmd/nginx/main.go	21.37% <0%> (-2.07%)	⬇️

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[antoineco]

/lgtm

[aledbf]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, antoineco, snelis

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[aledbf]

@snelis thanks!