Set transport.Version via ldflags for release

[jonjohnsonjr]

For most things consuming this package, they will depend on an actual
released version of go-containerregistry. When we release
go-containerregistry itself, the binaries are built at the same version
as the library, which means that they don't depend on an actual released
version of go-containerregistry, so the version in debug info is just
"(devel)". For our own release, we will just set it to the tag.

---

Tested via:

$ goreleaser --snapshot --skip-publish --rm-dist && ./dist/crane_linux_amd64/crane ls -v ubuntu 2>&1 | grep -i agent
User-Agent: crane/v0.2.1-next go-containerregistry/v0.2.1-next
User-Agent: crane/v0.2.1-next go-containerregistry/v0.2.1-next
User-Agent: crane/v0.2.1-next go-containerregistry/v0.2.1-next

Before:

$ goreleaser --snapshot --skip-publish --rm-dist && ./dist/crane_linux_amd64/crane ls -v ubuntu 2>&1 | grep -i agent
User-Agent: crane/v0.2.1-next go-containerregistry/(devel)
User-Agent: crane/v0.2.1-next go-containerregistry/(devel)
User-Agent: crane/v0.2.1-next go-containerregistry/(devel)

The real test will be looking at the UA of a downstream module to make sure the buildinfo stuff works.

[codecov-io]

Codecov Report

Merging #856 (4950c9b) into master (f937abd) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #856      +/-   ##
==========================================
- Coverage   74.32%   74.29%   -0.04%     
==========================================
  Files         106      106              
  Lines        4452     4454       +2     
==========================================
  Hits         3309     3309              
- Misses        650      651       +1     
- Partials      493      494       +1     

Impacted Files	Coverage Δ
pkg/v1/remote/transport/useragent.go	47.61% <0.00%> (-5.02%)	⬇️

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