Add a SiwG button placement setting to allow the button to be placed below the log in page modal

## Feature Description

Add a setting within the Sign in with Google module settings to allow the user to choose if they want the button placed above or below the WordPress login page modal.

Although this can be done via CSS styling, this would be a much more user friendly way to do this.

This was requested in the support forum: https://wordpress.org/support/topic/relocate-google-sign-in-button/

Current default:

Example of the button placed below:

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## Acceptance criteria

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## Implementation Brief

* [ ]

### Test Coverage

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## QA Brief

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## Changelog entry

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Start by locating the Sign in with Google module settings and the code that renders its button on the WordPress login page modal. Add a setting for above or below placement, then verify that both choices position the button correctly and that the existing placement remains the default.

Written by the indexing model from the issue text.