[IRD] Updated setup.sh and doc fixes in run-multiple-apps.md

[jessicaearayil]

Description

• Removed duplicate artifact download in script or each instance. It is now called for only each sample app in config.yml for multi-instance setup
• Updated run-multiple-apps.md docs for all sample apps such that it mentions environment variables to be edited in the env files of only the sample apps present in the config.yml

Fixes # (issue)

Any Newly Introduced Dependencies

None

How Has This Been Tested?

Checklist:

• I agree to use the APACHE-2.0 license for my code changes.
• I have not introduced any 3rd party components incompatible with APACHE-2.0.
• I have not included any company confidential information, trade secret, password or security token.
• I have performed a self-review of my code.