Add desired sharding keys for audit_events

Add desired sharding keys for feature category `audit_events`.

These tables have been identified as a [cell local tables](https://docs.gitlab.com/ee/development/database/multiple_databases.html#guidelines-on-choosing-between-gitlab_main_cell-and-gitlab_main_clusterwide-schema).
All cell local tables require a [sharding key](https://docs.gitlab.com/ee/development/database/multiple_databases.html#defining-a-sharding-key-for-all-cell-local-tables)
or a [desired sharding key](https://docs.gitlab.com/ee/development/database/multiple_databases.html#defining-a-desired_sharding_key-for-automatically-backfilling-a-sharding_key)

A desired sharding key has been automatically selected for these tables.
These keys were chosen as the desired sharding keys because the
table has a :belongs_to relationship to a table that itself has a `NOT NULL` sharding key.

Additionally, `gitlab_schema` has been set to `gitlab_main_cell` for any tables didn't use this schema already.
For these tables we have also added `allow_cross_joins`, `allow_cross_transactions` and
`allow_cross_foreign_keys`. These will silence any existing violations, allowing the pipeline to pass without
requiring further changes. In the future, we'll remove these `allow_...` statements and fix any violations as
they arise. You can read more about this in the [documentation for multiple databases](https://docs.gitlab.com/ee/development/database/multiple_databases.html)

We have assigned a random backend engineer from ~"group::compliance" to review these changes.

Please confirm that:

- each of these tables can be classified as cell local
- the selected desired sharding key is appropriate
- the backfill configuration for the desired sharding key is correct

When you are finished, please request a review from the database maintainer suggested by Danger.
If you have any questions or concerns, reach out to @tigerwnz or @manojmj.

If you would like to go through similar merged MRs so as to gather an understanding on this topic, you
can use [this](https://gitlab.com/gitlab-org/gitlab/-/merge_requests?scope=all&state=merged&label_name[]=automation%3Agitlab-housekeeper-authored) link.

This change was generated by
[gitlab-housekeeper](https://gitlab.com/gitlab-org/gitlab/-/tree/master/gems/gitlab-housekeeper)
using the Keeps::DetermineDesiredShardingKeyFeatureCategory keep.

To provide feedback on your experience with `gitlab-housekeeper` please comment in
<#442003>.

Changelog: other

db/docs/audit_events_streaming_event_type_filters.yml

 ---
 table_name: audit_events_streaming_event_type_filters
 classes:
-  - AuditEvents::Streaming::EventTypeFilter
+- AuditEvents::Streaming::EventTypeFilter
 feature_categories:
-  - audit_events
+- audit_events
 description: Represents a event type filter for audit event streaming
 introduced_by_url:
 milestone: '15.6'
-gitlab_schema: gitlab_main
+gitlab_schema: gitlab_main_cell
+allow_cross_joins:
+- gitlab_main_clusterwide
+allow_cross_transactions:
+- gitlab_main_clusterwide
+allow_cross_foreign_keys:
+- gitlab_main_clusterwide
+desired_sharding_key:
+  group_id:
+    references: namespaces
+    backfill_via:
+      parent:
+        foreign_key: external_audit_event_destination_id
+        table: audit_events_external_audit_event_destinations
+        sharding_key: namespace_id
+        belongs_to: external_audit_event_destination

db/docs/audit_events_streaming_headers.yml

 ---
 table_name: audit_events_streaming_headers
 classes:
-  - AuditEvents::Streaming::Header
+- AuditEvents::Streaming::Header
 feature_categories:
-  - audit_events
+- audit_events
 description: Represents a HTTP header sent with streaming audit events
 introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/88063
 milestone: '15.1'
-gitlab_schema: gitlab_main
+gitlab_schema: gitlab_main_cell
+allow_cross_joins:
+- gitlab_main_clusterwide
+allow_cross_transactions:
+- gitlab_main_clusterwide
+allow_cross_foreign_keys:
+- gitlab_main_clusterwide
+desired_sharding_key:
+  group_id:
+    references: namespaces
+    backfill_via:
+      parent:
+        foreign_key: external_audit_event_destination_id
+        table: audit_events_external_audit_event_destinations
+        sharding_key: namespace_id
+        belongs_to: external_audit_event_destination