Improve error message about global Jib config and update CHANGELOGs

[chanseokoh]

Closes #3138.

From #2996,

• Previously, any error from handling config.json was a warning and didn't cause a build to fail. Now we consider this as loading a global config, a build will fail if the code cannot load it.

Also updated the error message. The user in #3138 mistakenly thought they have to create the file manually.

[codecov]

Codecov Report

Merging #3144 (52460a9) into master (f8bc2e5) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #3144   +/-   ##
=========================================
  Coverage     71.08%   71.08%           
  Complexity     2320     2320           
=========================================
  Files           280      280           
  Lines          9825     9825           
  Branches        992      992           
=========================================
  Hits           6984     6984           
  Misses         2495     2495           
  Partials        346      346           

Impacted Files	Coverage Δ	Complexity Δ
.../jib/plugins/common/globalconfig/GlobalConfig.java	82.50% <ø> (ø)	11.00 <0.00> (ø)

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