Style improvements in the 2FA page

What does this MR do and why?

Style improvements in the 2FA page

• Show errors as a sticky flash alerts, for consistency with other flash alerts in the page.
• The top outline of some buttons were hidden below the .settings-sticky-header-inner element.

Changelog: changed

References

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• Two Factor Auth page: Migrate components (!171943 - merged)

MR acceptance checklist

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Screenshots or screen recordings

before	after

How to set up and validate locally

1. Go to the 2FA page and enable OTP authenticator: /-/profile/two_factor_auth
2. Click on the Delete one-time password authenticator
3. Check if the outline of the button is cut.
4. Enter a wrong password and check the position of the alert.