Add reCAPTCHA to password reset and confirmation email forms

What does this MR do and why?

Fixes #339147.

We have CAPTCHAs on the sign-in and sign-up pages - we should also have them on confirmation and password reset pages to reduce abuse.

One difference between these new reCAPTCHAS and existing ones is here we will show them all the time, when reCAPTCHA is enabled. For sign-in we show it selectively upon so many failed attempts. However, for these new pages we really don't have any concept of 'failures' to go off of. Given these pages are used less frequently I don't think it will be too much of a hinderance for users. If we find it is, we can probably add some rate limit trigger later on.

I consolidated some of the generic logic in the RecaptchaHelper in hopes this helps us in the future, too. Otherwise, there is a bit of repetitive code. I'm not sure if there's a reasonable way to reduce that due to subtle differences. I'm open to feedback if someone spots other opportunities.

Screenshots or screen recordings

Password Reset

Before	After

Resend Confirmation

Before	After

How to set up and validate locally

Ensure you have reCAPTCHA configured according to https://docs.gitlab.com/ee/integration/recaptcha.html. Then, in your GDK/test instance, visit:

• /users/password/new
• /users/confirmation/new

Observe the CAPTCHA is shown and is required to submit the form.

MR acceptance checklist

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