Use reusuable release workflow in sigstore/sigstore

[k4leung4]

Signed-off-by: Kenny Leung kleung@chainguard.dev

Summary

Leverage the reusable Release workflow in sigstore/sigstore repo so releases will be cut in the same manner across Cosign|Rekor|Fulcio.

The reusable workflow is pending review in sigstore/sigstore#325

Before this workflow works, the included shell script needs to be executed to setup necessary workflow identity provider that grants the needed permissions to build and push the release.

Ticket Link

Fixes

Works toward fixing https://github.com/sigstore/public-good-instance/issues/50

Release Note

[codecov-commenter]

Codecov Report

Merging #729 (a32c750) into main (17c69a7) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #729      +/-   ##
==========================================
+ Coverage   47.58%   47.59%   +0.01%     
==========================================
  Files          65       66       +1     
  Lines        5670     5696      +26     
==========================================
+ Hits         2698     2711      +13     
- Misses       2683     2695      +12     
- Partials      289      290       +1     

Impacted Files	Coverage Δ
pkg/sharding/ranges.go	40.00% <0.00%> (-40.00%)	⬇️
pkg/types/helm/v0.0.1/entry.go	52.41% <0.00%> (-1.21%)	⬇️
pkg/sharding/log_index.go	100.00% <0.00%> (ø)
pkg/types/alpine/v0.0.1/entry.go	62.01% <0.00%> (+0.77%)	⬆️
cmd/rekor-server/app/flags.go	64.44% <0.00%> (+3.66%)	⬆️

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