Remove dependencies from pkg/util

[mtrmac]

Summary

We are maintaining a Rekor client that calls pkg/client, and we care about the size of the binary

Because pkg/client depends on pkg/util, all dependencies of pkg/util end in the binary; recently that has grown quite a bit.

So, move things that aren’t shared between clients and servers into other sub packages, either directly into the only users, or into new packages. See individual commit messages for details.

In our case, this saves 1.87 MB from a macOS binary, and should not affect the behavior of any users.

I certainly don’t have the full picture, so I’d be happy to adjust the final code locations and names however is necessary.

(It’s a bit tempting to completely eliminate the pkg/util subpackage, maybe by moving the truly shared parts into pkg/clientserver, and the test helpers into pkg/test; util is a name that attracts adding more and more dependencies over time. But this is enough for my purposes, and I’ll leave the design discussions of such a refactor to maintainers.)

Release Note

NONE

Documentation

N/A

[codecov]

Codecov Report

Merging #1469 (586c7e9) into main (d402c45) will increase coverage by 21.00%.
The diff coverage is 93.75%.

@@             Coverage Diff             @@
##             main    #1469       +/-   ##
===========================================
+ Coverage   43.37%   64.37%   +21.00%     
===========================================
  Files          74       80        +6     
  Lines        7436     7789      +353     
===========================================
+ Hits         3225     5014     +1789     
+ Misses       3873     2127     -1746     
- Partials      338      648      +310     

Flag	Coverage Δ
e2etests	48.24% <93.75%> (?)
unittests	44.69% <37.50%> (+1.32%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/trillianclient/trillian_client.go	66.17% <ø> (ø)
pkg/api/tlog.go	39.02% <75.00%> (+39.02%)	⬆️
cmd/rekor-cli/app/pflags.go	90.30% <100.00%> (ø)
cmd/rekor-cli/app/validate.go	100.00% <100.00%> (ø)
pkg/api/api.go	68.23% <100.00%> (+68.23%)	⬆️
pkg/api/entries.go	64.87% <100.00%> (+64.87%)	⬆️

... and 51 files with indirect coverage changes

[haydentherapper]

Looks good, thanks!