Fix #3192: Reloading With --update-env Option

[mkalygin]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	#3192
License	MIT
Doc PR	N/A

Hi, this is my first bug fix for pm2. I've been struggling with the issue described in #3192 for a long time. Previously, I used the following hack to make it work properly:

pm2 startOrReload ecosystem.config.cjs --env production && pm2 reload app_name --update-env

After reviewing the code, I believe I have found the actual cause of this bug. The environment gets overriden due to a wrong object extension in Utility.extendExtraConfig.

I'm open to any suggestions for improvements.

[CLAassistant]

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