JSON validation support in CI

Most of the openbmc repositories depend on JSON configuration files,
which are consumed by the respective daemons at runtime.

It's a good value add to catch the JSON validation errors early in the
repository CI itself.

By default, the CI would be picking config/eslint-global-config as the
default configuration to run the JSON validation. The default configuration
can be overridden by the presence of the .eslintrc.json file from the
repository for which the CI is running against.

Repositories cannot completely opt-out of the JSON validation, but they
choose to skip whatever files/folders they want using the .eslintignore
configuration file or, they can also write the rules in .eslintrc.json
config file to turn errors into warnings.

This commit brings in eslint & eslint-plugin-json which does only the
"json validation".

Visit the below link(s) for more details & various error's/warnings that
this plugin would report:
https://www.npmjs.com/package/eslint-plugin-json
https://github.com/azeemba/eslint-plugin-json

I have tested all the repos under openbmc with the eslint-global-config
and only two repos are breaking due to this change, they are already
fixed(please check the topic: "json-validation" for more details)

Testing Example :
1. Make a json bad by purposefully removing a comma

Running the json validator on the repo using it's config >

/home/manojeda/ci_test_area/pldm/configurations/fru_master.json
  19:26  error  Expected comma  json/*

✖ 1 problem (1 error, 0 warnings)

2. if the json is good, the validation proceeds fruther without
any issues.

Change-Id: I2c2c14b18bb626b1a5ab5d818b92d5ba370e1639
Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 86c51de..c8d1567 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -801,6 +801,8 @@
     libxml-simple-perl \
     rsync
 
+RUN npm install -g eslint@latest eslint-plugin-json@latest
+
 RUN update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-11 11 \
   --slave /usr/bin/g++ g++ /usr/bin/g++-11 \
   --slave /usr/bin/gcov gcov /usr/bin/gcov-11 \