[Improvements] Improve the default prompt and data loader util functions

[deshraj]

Description

Changes:

• Make changes in the default prompt to yield better answers and reduce hallucinations
• Rename var name 'meta_data' to 'metadata' for consistency
• Refactor the clean_string method to parse the context properly

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Refactor (does not change functionality, e.g. code style improvements, linting)

How Has This Been Tested?

• Unit Test

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (9a11683) 56.59% compared to head (e981d81) 56.58%.

Files	Patch %	Lines
embedchain/loaders/slack.py	0.00%	3 Missing ⚠️
embedchain/loaders/rss_feed.py	0.00%	2 Missing ⚠️
embedchain/loaders/unstructured_file.py	0.00%	2 Missing ⚠️
embedchain/loaders/discord.py	0.00%	1 Missing ⚠️
embedchain/loaders/text_file.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1272      +/-   ##
==========================================
- Coverage   56.59%   56.58%   -0.01%     
==========================================
  Files         146      146              
  Lines        5955     5954       -1     
==========================================
- Hits         3370     3369       -1     
  Misses       2585     2585              

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