Add tiiuae/falcon-7b-instruct model support to llm-combined

[aamajumder]

Describe your changes

Added the option to convert and run Falcon-7b-instruct using the llm.py script and the flag --model_type=falcon

Checklist before requesting a review

• Add unit tests for this change.
• Make sure all tests can pass.
• Update documents if necessary.
• Lint and apply fixes to your code by running lintrunner -a
• Is this a user-facing change? If yes, give a description of this change to be included in the release notes.

(Optional) Issue link

[aamajumder]

@microsoft-github-policy-service agree company="Microsoft"

[guotuofeng]

Please fix the lint errors.

[guotuofeng]

Please rebase from main.

[PatriceVignola]

Please rebase from main.

This is going into a feature branch that is not up-to-date with the main branch yet because of all the churn. We'll rebase the feature branch before merging it into main.

[guotuofeng]

it seems there are some conflict?