Changing the backend to query labels datasets

[shootinputin007]

Changes:

• Removed flipside related elements from requirements.txt, .env.sample file and simulate.py
• Added ENS_BIGQUERY_DATATABLE and LABELS_BIGQUERY_DATATABLE in the .env.sample file
• Removed query_flipside function and created a query_labels function that queries the LABELS_BIGQUERY_DATATABLE (eden-data-private.ethereum_auxiliary.flipside_labels) and ENS_BIGQUERY_DATATABLE (container-testing-381309.etherscan.account_tags) to get the address labels
• Removed the to_json function, as it became redundant
• Edited the fetch_address_labels and add_labels functions to match the new functions
• Edited simulate.py to 1) load LABELS_BIGQUERY_DATATABLE and ENS_BIGQUERY_DATATABLE from .env and 2) to pass the biquery_client to add_labels function