Add txt file as the new data loader

[taranjeet]

🚀 The feature

There should be a data loader to read txt files

Motivation, pitch

Support wider category of data

[eren-darici]

Hey! I think somebody already added.

[Dev-Khant]

It's already added https://github.com/embedchain/embedchain/blob/main/embedchain/loaders/text_file.py. Documentation is remaining.

[Dev-Khant]

Fixed here #1410