✨ Add Sftp source and Prefect tasks

[Diego-H-S]

Summary

SFTP connector migration from viadot 1 to viadot 2.

Importance

Required by the migration project.

Checklist

This PR:

• follows the guidelines laid out in CONTRIBUTING.md
• links relevant issue(s)
• adds/updates tests (if appropriate)
• adds/updates docstrings (if appropriate)
• adds an entry in CHANGELOG.md

[Diego-H-S]

have a look at them.

[trymzet]

Some of the feedback still needs to be addressed, otherwise I think 90% is either done or requires an issue to be created & linked.

[Rafalz13]

Tests are in progress. @trymzet please take a look at the code.

[trymzet]

2 minor things left. Also, pls make sure that CI passes before requesting PR, otherwise it's added work for me since I need to look at the same PR twice.