Add non-GCP PALM providers

[Mark-Zeng]

Description

Add new LLM and embedding providers for PALM (non-GCP)

Fixes #480

Type of change

• New feature (non-breaking change which adds functionality)
• Documentation update

How Has This Been Tested?

Since the new embedder and llm uses API, the test is done manually by adding data and sending queries.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

Maintainer Checklist

• closes Feature Request: Add support for Palm LLM Models/Embeddings #480
• Made sure Checks passed

[deshraj]

Thanks @Mark-Zeng for the contribution. I reviewed the PR and it looks good in general apart from small bugs.

You can fix these bugs by cherry picking this commit in your PR: d2a3acd

Also, please rebase after cherry picking so that we can merge your PR. Thanks!

[Dev-Khant]

@Mark-Zeng Can you please resolve the merge conflicts so we can merge the PR?

[deshraj]

Closing this PR because of inactivity.