Rename "Create Category" button to make it distinct from "Assign Category" link/action

[mrfoxtalbot]

Steps to reproduce the behavior

1. Edit any post and add go to add a new category under Categories -> "Add New Category"
2. When creating a new category, the button to actually save the change is also titled "Add New Category"

What I expected to happen

This should be labeled something like "Save new category" to make it distinct from the initial link to add a new category so it's clear the user has to use it to click on it to create and assign this new term.

Context

We have had users run into this issue not realizing they have to click a button titled "Add new category" a second time. They were then confused when the "Update" or "Publish" button didn't become available.

[mrfoxtalbot]

We might want to take into account this other issue too #28577