Add support for File Input element type

[cleavenworth]

Slack added a file_input input element type with an API update in January 2024. This PR would add support for the file_input element in the builder.

[imryche]

Hi! Thank you for the contribution. Please take a look at the few comments that I've left. I'll merge the PR immediately after they are addressed.

[cleavenworth]

@imryche Thanks for pointing that out. I've updated the branch with those recommended changes.

[imryche]

I think we should inherit from the ActionableComponent class to make the tests pass

[cleavenworth]

Looks like I left a reference to focus_on_load in test_elements.py. I've removed that and also implemented the change to use ActionableComponent.

[imryche]

Released the changes in v1.8.0