feat: add user account verification (#2190)

* add verified column to users table

* add database functions to check if verified, or to verify

* getting there

* verification check

* use base64 urlsafe no pad

* add verification client

* clippy

* correct docs

* fix integration tests

crates/atuin-server-postgres/migrations/20240621110731_user-verified.sql

@@ -0,0 +1,8 @@
+alter table users add verified_at timestamp with time zone default null;
+
+create table user_verification_token(
+  id bigserial primary key, 
+  user_id bigint unique references users(id), 
+  token text, 
+  valid_until timestamp with time zone
+);