Add geetest captcha

What does this MR do and why?

This MR is frontend part of #1746 (closed)

Screenshots or screen recordings

Scenario 1	Scenario 2	Scenario 3
		same with scenario 2

How to set up and validate locally

1. Merge geetest_captcha_backend branch into replace-tencent-captcha-to-geetest
2. Start GDK with GEETEST_CAPTCHA_ID='ask MR author for it' GEETEST_CAPTCHA_KEY='ask MR author for it'
3. Enable FF

Feature.enable(:geetest_captcha)

4. Enter http://127.0.0.1:3000/admin/application_settings/reporting
5. Config(register reCAPTCHA and Akismet, ask MR author for the keys)
6. Refresh login page serveral times (scenario 1)
7. Create code snippets named 123123test (scenario 2)
8. Enable realname(you can hardcode jh/lib/gitlab/real_name_system.rb to true) (scenario 3)

MR acceptance checklist

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