Add metric for the count of skaffold configurations in current session; fix the build platform type metric to save list of all platforms

[gsquared94]

Fixes #5329

[codecov]

Codecov Report

Merging #5437 (1c84d3c) into master (1a93be5) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #5437      +/-   ##
==========================================
- Coverage   71.40%   71.38%   -0.02%     
==========================================
  Files         397      397              
  Lines       14543    14549       +6     
==========================================
+ Hits        10384    10386       +2     
- Misses       3388     3390       +2     
- Partials      771      773       +2     

Impacted Files	Coverage Δ
pkg/skaffold/instrumentation/types.go	0.00% <ø> (ø)
pkg/skaffold/instrumentation/export.go	76.92% <100.00%> (+0.17%)	⬆️
pkg/skaffold/instrumentation/meter.go	58.06% <100.00%> (+8.06%)	⬆️
pkg/skaffold/util/tar.go	50.66% <0.00%> (-5.34%)	⬇️

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[MarlonGamez]

LGTM