feat: invoke verbose metadata

[lkingland]

Changes

• 🎁 invoke -v prints metadata

HTTP headers or CloudEvent fields are printed on invoke with verbose enabled.

$ func invoke --verbose
"Content-Type":text/plain; charset=utf-8
"Date":Tue, 05 Apr 2022 14:02:10 GMT
"Content-Length":3

OK

/kind enhancement

Fixes #922

[knative-prow]

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[codecov]

Codecov Report

Merging #944 (420ed98) into main (739cded) will increase coverage by 1.98%.
The diff coverage is 37.50%.

@@            Coverage Diff             @@
##             main     #944      +/-   ##
==========================================
+ Coverage   43.85%   45.83%   +1.98%     
==========================================
  Files          55       57       +2     
  Lines        5163     7442    +2279     
==========================================
+ Hits         2264     3411    +1147     
- Misses       2576     3703    +1127     
- Partials      323      328       +5     

Impacted Files	Coverage Δ
cmd/invoke.go	34.81% <0.00%> (-0.97%)	⬇️
invoke.go	52.99% <61.53%> (+2.99%)	⬆️
client.go	61.94% <100.00%> (+2.01%)	⬆️
cmd/list.go	56.25% <0.00%> (-3.40%)	⬇️
cmd/info.go	24.77% <0.00%> (-2.38%)	⬇️
function_buildtype.go	92.30% <0.00%> (-2.14%)	⬇️
cmd/run.go	71.42% <0.00%> (-1.30%)	⬇️
k8s/secrets.go	13.54% <0.00%> (-0.75%)	⬇️
templates.go	79.41% <0.00%> (-0.59%)	⬇️
instances.go	29.50% <0.00%> (-0.50%)	⬇️
... and 50 more

---

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[lance]

Overall looks great, but I recommend some changes to the output for event invocation, and I've made a small suggestion for the output formatting.

[lance]

/lgtm