Sharepoint - multiple files logic applied to the source class (#942)

* ⬆️ Relax sql-metadata version requirement (#940)

* ⬆️ Relax sql-metadata version requirement

* 📌 Update lockfiles

* ✨ Added `validate_and_reorder_dfs_columns` to utils

* ♻️ Added new version of Sharepoint source class with additional functions

* ✅ added tests for `validate_and_reorder_dfs_columns` function

* ✅ Created `sharepoint_mock` function and changed function name to `_download_file_stream`

* 📝 Updated docstring for Sharepoint source class and functions

* ⬆️ Relax sql-metadata version requirement (#940)

* ⬆️ Relax sql-metadata version requirement

* 📌 Update lockfiles

* 🚧 Modified `validate_and_reorder_dfs_columns`

* 🐛 Added `na_values` to `_load_and_parse` function

* 🐛 Added tests for Sharepoint functions

* 🐛 Added **kwargs to handle_multiple_files function

* 🚧 Added `dtypes=str` instead of functions

* ✅  Removed tests for not existing functions

* ✅ Added missing tests

* ✅ Added missing tests to sharepoint class methods

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Co-authored-by: Michał Zawadzki <[email protected]>
Co-authored-by: Marcin Purtak <[email protected]>