Enable gofumpt linter

[sunjayBhatia]

A stricter form of gofmt, added rules can be found here: https://github.com/mvdan/gofumpt?tab=readme-ov-file#added-rules

[sunjayBhatia]

can run gofumpt -l -w -extra . to repro the changes

[codecov]

Codecov Report

Attention: 13 lines in your changes are missing coverage. Please review.

Comparison is base (02faa3a) 78.81% compared to head (c3a710b) 78.85%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6093      +/-   ##
==========================================
+ Coverage   78.81%   78.85%   +0.03%     
==========================================
  Files         138      138              
  Lines       19778    19731      -47     
==========================================
- Hits        15589    15558      -31     
+ Misses       3886     3870      -16     
  Partials      303      303              

Files	Coverage Δ
cmd/contour/certgen.go	50.72% <ø> (ø)
cmd/contour/contour.go	0.00% <ø> (ø)
cmd/contour/shutdownmanager.go	42.93% <ø> (+0.71%)	⬆️
internal/annotation/annotations.go	100.00% <100.00%> (ø)
internal/certgen/certgen.go	74.45% <100.00%> (ø)
internal/certgen/output.go	48.48% <100.00%> (-1.52%)	⬇️
internal/contour/metrics.go	71.21% <100.00%> (ø)
internal/controller/grpcroute.go	26.66% <ø> (+0.86%)	⬆️
internal/controller/httproute.go	26.66% <ø> (+0.86%)	⬆️
internal/controller/tcproute.go	0.00% <ø> (ø)
... and 41 more

[skriss]

The changes all look reasonable to me. It'd be nice to add a make task to use gofumpt to auto-format everything and maybe mention it in CONTRIBUTING.md

[skriss]

👍