Enable registry mirrors in Jib CLI

[mpeddada1]

Fixes #3047.

Did a manual test similar to the one described in #3011 with this config.json:

{"disableUpdateCheck":false,
 "registryMirrors": [
    {
      "registry": "registry-1.docker.io",
      "mirrors": ["mirror.gcr.io", "localhost:5000"]
    }
]
}

(Case where we fall back to Docker Hub):
It first tries mirror.gcr.io and if the base image is not found then it tries localhost:5000. It fails on localhost:5000 with a connection error but doesn't fail the entire build. It finally pulls from Docker Hub.

(Case where we pull from mirror.gcr.io):
And using --from=busybox for example, results in the image being pulled from mirror.gcr.io.

[codecov]

Codecov Report

Merging #3134 (c5b916b) into master (17a333e) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #3134      +/-   ##
============================================
- Coverage     71.07%   71.04%   -0.03%     
  Complexity     2319     2319              
============================================
  Files           280      280              
  Lines          9819     9823       +4     
  Branches        992      992              
============================================
  Hits           6979     6979              
- Misses         2494     2498       +4     
  Partials        346      346              

Impacted Files	Coverage Δ	Complexity Δ
...ain/java/com/google/cloud/tools/jib/cli/Build.java	18.91% <0.00%> (-1.09%)	4.00 <0.00> (ø)
.../main/java/com/google/cloud/tools/jib/cli/Jar.java	43.75% <0.00%> (-1.42%)	14.00 <0.00> (ø)

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[chanseokoh]

Let's update CHANGELOG.

And in a separate PR, update the CLI README about configuring the registry mirror like in the plugins doc.