Add Cohere LLM support

[sidmohanty11]

Description

This PR adds Cohere LLM support in Embedchain

Fixes #684

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (does not change functionality, e.g. code style improvements, linting)
• Documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Please delete options that are not relevant.

• Unit Test
• Test Script (please provide)

Test Script

from embedchain import App
from embedchain.llm.cohere import CohereLlm
import os

os.environ["OPENAI_API_KEY"] ="sk-xxx"
os.environ["COHERE_API_KEY"] = "xxx"

app = App(
    llm=CohereLlm(),
)

app.add("https://en.wikipedia.org/wiki/Pok%C3%A9mon")

response = app.query("What is a pokemon?")

print("Answer: ", response)

Output:

Answer:   Pokemon are creatures that co-exist with humans in the Pokemon universe. There are many different types of Pokemon, each with its own unique abilities and powers. Pokemon are trained and captured by their owners and can be used to battle one another.

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 #xxxx (Replace xxxx with the GitHub issue number)
• Made sure Checks passed

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
embedchain/llm/cohere.py	84.00% <84.00%> (ø)

📢 Thoughts on this report? Let us know!.