Migrate from template to prompt arg while keeping backward compatibility

[sidmohanty11]

Description

This PR aims to migrate from the previously called template arg to prompt

Type of change

• 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)

import os
from embedchain import Pipeline as App
from embedchain.config.llm.base import BaseLlmConfig

os.environ["OPENAI_API_KEY"] = "sk-xxx"
app = App.from_config(config={
    "llm": {
        "config": {
# generates warning
            "template": "The user's name is Sidharth, always greet him with 'Hello Sidharth' or 'Good Morning Sid'. Context $context Query $query Helpful Answer:",
        }
    }
})

print(app.query("what is the weather like today?"))

import os
from embedchain import Pipeline as App
from embedchain.config.llm.base import BaseLlmConfig

os.environ["OPENAI_API_KEY"] = "sk-xxx"
app = App.from_config(config={
    "llm": {
        "config": {
# the new way
            "prompt": "The user's name is Sidharth, always greet him with 'Hello Sidharth' or 'Good Morning Sid'. Context $context Query $query Helpful Answer:",
        }
    }
})

print(app.query("what is the weather like today?"))

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.

Comparison is base (6c1ea77) 58.47% compared to head (780129b) 58.51%.

Files	Patch %	Lines
embedchain/llm/base.py	62.50%	3 Missing ⚠️
embedchain/config/llm/base.py	93.75%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1066      +/-   ##
==========================================
+ Coverage   58.47%   58.51%   +0.04%     
==========================================
  Files         129      129              
  Lines        5021     5026       +5     
==========================================
+ Hits         2936     2941       +5     
  Misses       2085     2085              

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