improvement: twilio autopilot:fields:delete

[pranavdesh]

This command currently requires the fieldTypeSid which is incorrect. The API actually requires the field SID. In addition to changing that, propose the following changes to improve usability:

• Make assistant SID the only required argument. Field sid and task sid can be optional.
• If the user does not provide field sid and task sid, then list all tasks by their unique name and ask the user to select the task the field they want to delete belongs to
• then list all fields under that task and ask the user to pick the one they want to delete.
• if the field is used in one or more samples, the API will not allow us to delete it. Make sure to handle this error and display a message telling the developer to first delete samples under this task.

[pranavdesh]

Functionality works. Please change the first bit of text displayed to - 'Choose the Task your Field belongs to: ' and the second bit to 'Choose the Field to delete:'