[native] Minor updates to KeyserverSelection TextInput

Summary:
While working on the TextInputs for UsernameSelection and PasswordSelection, I realized a couple updates I should make to the TextInput in KeyserverSelection:

1. Set onSubmitEditing, so that the user can use the software keyboard action button to proceed to the next screen.
2. Use returnKeyType="go" instead of the default "next". The latter matches the copy of our RegistrationButton, but is treated by the OS as more of a "next input field" button. Whereas "go" is meant for "I'm done with this page, go to the next one" and utilizes a design that indicates a more explicit action.

Test Plan:

1. I tested onSubmitEditing by pressing the button while the TextInput was empty (nothing happens, same as before) and while the TextInput was populated (proceeds to the next screen).
2. Here are screenshots for the returnKeyType change:

before	after

Reviewers: atul, ginsu

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7989