one-step install script with vanilla pt2.4 by default

[zyaoj]

What does this PR do? Please describe:
Add an one-step installation script with vanilla PT 2.4.

Fixes #848

Does your PR introduce any breaking changes? If yes, please list them:
List of all backwards-incompatible changes.

Check list:

• Was the content of this PR discussed and approved via a GitHub issue? (no need for typos or documentation improvements)
• Did you read the contributor guideline?
• Did you make sure that your PR does only one thing instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests?
• Did you verify new and existing tests pass locally with your changes?
• Did you update the CHANGELOG? (no need for typos, documentation, or minor internal changes)

Example

$ ./tools/install_basic.sh fairseq2_public_install --skip-apex
Creating 'fairseq2_public_install' Conda environment with PyTorch 2.4.0 and CUDA 12.1...
Channels:
 - conda-forge
Platform: linux-64
Collecting package metadata (repodata.json): done
Solving environment: done

<-- SKIP -->

Done!
To activate the environment, run 'conda activate fairseq2_public_install'.
To deactivate the environment, run 'conda deactivate'.
To delete the environment, run 'rm -rf /private/home/$USER/fairseq2/envs/fairseq2_public_install; rm -rf /private/home/$USER/miniconda3/envs/fairseq2_public_install'.
$ conda run -n fairseq2_public_install --live-stream fairseq2 assets list | grep llama3_1_8b
   - model:llama3_1_8b
   - model:llama3_1_8b_instruct
   - tokenizer:llama3_1_8b
   - tokenizer:llama3_1_8b_instruct
   - model:llama3_1_8b@awscluster
   - model:llama3_1_8b_instruct@faircluster
   - model:llama3_1_8b_instruct@awscluster
   - tokenizer:llama3_1_8b@awscluster
   - tokenizer:llama3_1_8b_instruct@faircluster
   - tokenizer:llama3_1_8b_instruct@awscluster

[zyaoj]

We will not to one-step installer for public-facing for now.