Consolidate and clean-up Fetch CSV file interactions

[oree-xx]

Fixes

• Fixes Consolidate and clean-up Fetch CSV file interactions #282

Description

• Cleaned up repeated write_to_sv functions in fetch scripts.
• Added rows_to_csv function to shared.py for appending data to csv file.
• Removed the initialise_data function in arxiv fetch script
• Changed the function name data_to_csv to dataframe_to_csv

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[TimidRobot]

This PR is looking great!

Please also update gcs_fetch.py to use shared.rows_to_csv() along with changes requested below.

[TimidRobot]

Just a few small fixes required

[TimidRobot]

great work, thank you!!