Updates "Submit" button with "Create runner"

What does this MR do and why?

Fixes #410544 (closed)

After inputting details of the runner the user to the next screen to register the runner, this step creates a new runner record.

Text in the "Submit" button is replaced with "Create runner" to convey this.

Changelog: changed

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. As admin
2. Visit Admin -> Runners
3. Select "New instance runner"
4. In the /new page (e.g. http://gdk.test:3000/top-group/top-project/-/runners/new)
5. Confirm the button is updated

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #410544 (closed)