add skaffold inspect build-env command

[gsquared94]

Add commands skaffold inspect build-env and skaffold inspect build-env list.

❯ skaffold inspect build-env          
Interact with skaffold build environment definitions.

Available Commands:
  list        Print the list of active build environments.

Use "skaffold <command> --help" for more information about a given command.

❯ skaffold inspect build-env list --help                    
Print the list of active build environments.

Examples:
  # Get list of target build environments with activated profiles p1 and p2
  skaffold inspect build-env list -p p1,p2 --format json

Options:
  -p, --profile=[]: Profile names to activate

Usage:
  skaffold inspect build-env list [flags] [options]

Use "skaffold options" for a list of global command-line options (applies to all
commands).

Run in examples/buildpacks directory:

❯ skaffold inspect build-env list | jq
{
  "build_envs": [
    {
      "type": "local",
      "path": "/Users/gaghosh/Code/Work/fork/skaffold/examples/buildpacks/skaffold.yaml"
    }
  ]
}

[codecov]

Codecov Report

Merging #5792 (0f21129) into master (efd6c5b) will increase coverage by 0.11%.
The diff coverage is 96.66%.

@@            Coverage Diff             @@
##           master    #5792      +/-   ##
==========================================
+ Coverage   70.75%   70.86%   +0.11%     
==========================================
  Files         436      438       +2     
  Lines       16308    16374      +66     
==========================================
+ Hits        11539    11604      +65     
+ Misses       3919     3917       -2     
- Partials      850      853       +3     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/inspect_build_env.go	91.66% <91.66%> (ø)
cmd/skaffold/app/cmd/inspect.go	100.00% <100.00%> (ø)
pkg/skaffold/inspect/build_env.go	100.00% <100.00%> (ø)
pkg/skaffold/inspect/profiles.go	100.00% <100.00%> (ø)
pkg/skaffold/inspect/types.go	100.00% <100.00%> (+54.54%)	⬆️
pkg/skaffold/schema/profiles.go	88.46% <0.00%> (-1.15%)	⬇️
pkg/skaffold/parser/config.go	79.56% <0.00%> (-0.13%)	⬇️
pkg/skaffold/schema/errors/errors.go	100.00% <0.00%> (ø)
... and 1 more

---

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[MarlonGamez]

looks good to me 👍🏼