Add user_access_locked audit event

What does this MR do and why?

Resolves Add audit event when user access is locked after exceeding failed sign-in attempts limit as part of https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/244+

This MR adds user_access_locked audit event type triggered when a user's access to the instance is locked. This can happen, for example, when the user exceeds the allowed number of failed login attempts.

Aside from the main purpose of audit event records, this audit event will also be used to show a history of a user's auth states in the admin user page.

Screenshots or screen recordings

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How to set up and validate locally

1. With a new user or an existing one, login with an incorrect password 4 times.

2. Validate that no audit event is created

   Replace test615 with the username of your GDK user

   $ rails console
   > AuditEvent.by_entity_username('test615')
   => []
   >

3. Login one more time with an incorrect password

4. Validate that an audit event with correct attributes is created.

   Replace test615 with the username of your GDK user

   attribute	expected value
   entity_path	"test615"
   author_name	"GitLab Admin Bot"
   details.custom_message	"User access locked - excessive failed login attempts"

   $ rails console
   > AuditEvent.by_entity_username('test615')
   => [#<AuditEvent:0x000000012a727e98
     id: 615,
     author_id: 173,
     entity_id: 172,
     entity_type: "User",
     details:
      {:author_name=>"GitLab Admin Bot",
       :author_class=>"User",
       :target_id=>172,
       :target_type=>"User",
       :target_details=>"t t",
       :custom_message=>"User access locked - excessive failed login attempts",
       :ip_address=>"127.0.0.1",
       :entity_path=>"test615"},
     ip_address: #<IPAddr: IPv4:127.0.0.1/255.255.255.255>,
     author_name: "GitLab Admin Bot",
     entity_path: "test615",
     target_details: "t t",
     created_at: Wed, 21 Jun 2023 02:03:16.878321000 UTC +00:00,
     target_type: "User",
     target_id: 172>]
   >

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