Multiple optimizations to build targets

[antoineco]

What this PR does / why we need it:

• Clean up e2e test on interruption
  Currently, interrupting Ginkgo does not clean up the namespaces created as part of the e2e tests.
• Leverage GOCACHE for faster builds
  Speeds up Docker-based builds significantly.
• Forward container STDIN in make targets
  Actually do something when the user presses Ctrl+C.

/assign @aledbf @ElvinEfendi

[aledbf]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[aledbf]

@antoineco thanks!

[codecov-io]

Codecov Report

Merging #2823 into master will increase coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2823      +/-   ##
==========================================
+ Coverage   47.34%   47.45%   +0.11%     
==========================================
  Files          75       75              
  Lines        5413     5413              
==========================================
+ Hits         2563     2569       +6     
+ Misses       2525     2521       -4     
+ Partials      325      323       -2

Impacted Files	Coverage Δ
internal/watch/file_watcher.go	80.76% <0%> (-3.85%)	⬇️
cmd/nginx/main.go	11.18% <0%> (+4.6%)	⬆️

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