removed most of the warnings from Dockerfile when running docker build

[resoluteCoder]

This PR removes most of the warnings when building the container image using docker build.

Previous Warnings:

 10 warnings found (use --debug to expand):
 - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 8)
 - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 25)
 - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 38)
 - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 42)
 - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 46)
 - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 51)
 - UndefinedVar: Usage of undefined variable '$CONFIG_FILE' (line 28)
 - UndefinedVar: Usage of undefined variable '$CONFIG_FILE' (line 54)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 66)
 - JSONArgsRecommended: JSON arguments recommended for CMD to prevent unintended behavior related to OS signals (line 68)

Currently:

 2 warnings found (use --debug to expand):
 - UndefinedVar: Usage of undefined variable '$CONFIG_FILE' (line 28)
 - UndefinedVar: Usage of undefined variable '$CONFIG_FILE' (line 54)

[evaline-ju]

LGTM - thanks for the update!