Implement CAPTCHA configuration estimation from avg, peak and

broke_my_site_traffic

The above metrics are sourced from the user and are stored in the
database to reuse at a later point in time when the mCaptcha instance's
admin changes suggested configuration.

I'm not sure if I want to recompute configuration every time the admin
updates suggested configurations or give the user an option to recompute
based on latest trends. If we recompute on every update, then should the
admin choose very high difficulty_factors then it would hold back the
user's visitors, which is not nice. But there should also be an option
to rerun estimates when older configuration no longer works properly.

migrations/20211202141927_mcaptcha_sitekey_user_provided_avg_traffic.sql

@@ -0,0 +1,6 @@
+CREATE TABLE IF NOT EXISTS mcaptcha_sitekey_user_provided_avg_traffic (
+	config_id INTEGER PRIMARY KEY UNIQUE NOT NULL references mcaptcha_config(config_id)  ON DELETE CASCADE,
+	avg_traffic INTEGER DEFAULT NULL,
+	peak_sustainable_traffic INTEGER DEFAULT NULL,
+	broke_my_site_traffic INTEGER DEFAULT NULL
+);