Sign-in form improvements

What does this MR do and why?

• Reduce and simplify classes related to the vertical and horizontal spaces. Remove padding in each individual element by adding padding to the parent form.

• Make the Sign in button Pajamas compliant.

• Maintain the checkbox close to the Sign in button.

• Remove unnecessary HAML partial

• Improve internationalization.

Changelog: changed

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2. To enable arkoselabs captcha: !82737 (merged)

MR acceptance checklist

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