Improve dataloader error handling

[miararoy]

Problem

data loading has no meaningful error handling, albeit being a sensitive part of the flow

resolves: #181

Solution

first, defining DataLoaderException that will formalize all data loading error on both the file/row level and unify them under one error, then change the exception handling to raise this error

Type of Change

• 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)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

• adding simple tests for data loading of .txt
• changing the current mechanism of dataloader tests to also have the data as (name, df, exception) for the bad cases

note that tests should were added to txt -> df as from df to documents is handled.

[igiloh-pinecone]

@miararoy see a few suggestions please

[igiloh-pinecone]

LGTM