feat: function creation timestamp

[lkingland]

Changes

• 🎁 function creation timestamp

It is becoming clear that a timestamp of when a Function successfully completed the creation process will be valuable. In particular this will help with a few forthcoming PRs currently WIP, I'm separating this into its own PR to solicit feedback such as consequences unanticipated.

[codecov]

Codecov Report

Merging #651 (1ed925b) into main (fc1e874) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #651      +/-   ##
==========================================
+ Coverage   36.26%   36.31%   +0.04%     
==========================================
  Files          38       38              
  Lines        3847     3850       +3     
==========================================
+ Hits         1395     1398       +3     
  Misses       2268     2268              
  Partials      184      184              

Impacted Files	Coverage Δ
function.go	57.57% <ø> (ø)
client.go	60.53% <100.00%> (+0.17%)	⬆️
config.go	62.13% <100.00%> (+0.31%)	⬆️

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[lance]

/lgtm
/approve

[knative-prow-robot]

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