The concept of alternate_url is fundamentally flawed, so
we are removing it before it is released.

https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10609

This change allows to use some alternative URL for primary node.
This URL will be used only by secondary node to reach the primary

Add the form field, and allow the data to flow through to the model
just like the regular `url` field.

Hashed storage is now a requirement of Geo. This is
one part of deprecating non-hashed storage for Geo.

This commit add a minimum_reverification_interval column to
the geo_nodes table. This columns says after how many days
(at least) a repository should reverified.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Closes #3948