Update go module to v2

[sjberman]

Problem: With the release of v2.0 of NGINX Gateway Fabric, we need to update the go module version to include /v2, per Go module import standards. Otherwise, NGF cannot be imported past v1.

Solution: Update the module version and all imports to v2.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

Update Go module to v2

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.06%. Comparing base (9308f2c) to head (e580cff).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3660      +/-   ##
==========================================
- Coverage   87.06%   87.06%   -0.01%     
==========================================
  Files         127      127              
  Lines       15580    15580              
  Branches       62       62              
==========================================
- Hits        13565    13564       -1     
- Misses       1857     1858       +1     
  Partials      158      158              

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