Allow setting null for connection pool size (#50726)

## Context

Allows users to "reset" the value for connection pool size in pooler
configuration under [database
settings](http://supabase.com/dashboard/project/_/database/settings)
<img width="500" alt="image"
src="https://github.com/user-attachments/assets/4eb98088-1898-423c-8ef6-655fd0573601"
/>

Refer to the [Linear
ticket](https://linear.app/supabase/issue/FE-4425/support-setting-null-for-pool-size-in-pooler-config)
for more details about why this change is needed - its a bit of an
explanation 😅 🙏

## To test
- [ ] Verify that you can save a pool size, and that the GET
`/config/pgbouncer` network request returns `default_pool_size` property
in its response
- [ ] Verify that you can save while leaving the pool size input field
empty, and that the GET `/config/pgbouncer` network request thereafter
doesn't return `default_pool_size` in its response

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Preserved the intended database connection pool setting when no
default pool size is specified, rather than automatically applying a
compute-size-based value.
  * Explicitly entered pool sizes continue to be saved unchanged.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/studio/components/interfaces/Settings/Database/ConnectionPooling/ConnectionPooling.tsx

@@ -129,7 +129,7 @@ export const ConnectionPooling = () => {
     updatePoolerConfig(
       {
         ref: projectRef,
-        default_pool_size: default_pool_size === undefined ? defaultPoolSize : default_pool_size,
+        default_pool_size: default_pool_size === undefined ? null : default_pool_size,
         ignore_startup_parameters: ignoreStartupParameters ?? '',
       },
       {

packages/api-types/types/platform.d.ts

@@ -6326,6 +6326,10 @@ export interface components {
       branch_limit?: number
       installation_id: number
       new_branch_per_pr?: boolean
+      /**
+       * @description Project ref
+       * @example abcdefghijklmnopqrst
+       */
       project_ref: string
       repository_id: number
       supabase_changes_only?: boolean
@@ -7851,6 +7855,10 @@ export interface components {
         metadata: {
           [key: string]: unknown
         }
+        /**
+         * @description Project ref
+         * @example abcdefghijklmnopqrst
+         */
         supabase_project_ref: string
       }
       organization_integration_id: string
@@ -7861,6 +7869,10 @@ export interface components {
       metadata: {
         [key: string]: unknown
       }
+      /**
+       * @description Organization slug
+       * @example tsrqponmlkjihgfedcba
+       */
       organization_slug: string
       source: string
       teamId?: string