track other ddl commands in neon_ddl_handler

[ruslantalpa]

Problem

The new rest broker service (neon proxy) added in this pr needs a way to be notified of schema changes (similar events to a ddl_command_end trigger) to refresh it's cache. We can't use the trigger+notify approach here because of scale to zero.

Summary of changes

Added a way to track the total number of ddl commands with other_ddl_count; counter in ddlHashTable since we are not interested in specifics, just that the schema changed.

The shape of the json sent to the control plane will look like this

{
  "dbs": [
    ...
  ],
  "roles": [
    ...
  ],
  "other": 15. <--- the new key
}

[github-actions]

If this PR added a GUC in the Postgres fork or neon extension,
please regenerate the Postgres settings in the cloud repo:

make NEON_WORKDIR=path/to/neon/checkout \
  -C goapp/internal/shareddomain/postgres generate

If you're an external contributor, a Neon employee will assist in
making sure this step is done.

[github-actions]

8976 tests run: 8327 passed, 0 failed, 649 skipped (full report)

---

Flaky tests (15)

Postgres 17

• test_hot_standby_gc[True]: release-x86-64-without-lfc
• test_tx_abort_with_many_relations[v1]: release-arm64-without-lfc, release-arm64-with-lfc
• test_tx_abort_with_many_relations[v2]: release-arm64-without-lfc
• test_cancellations: release-arm64-with-lfc
• test_sharding_split_failures[failure2]: release-arm64-with-lfc
• test_sharding_split_failures[failure9]: release-arm64-with-lfc
• test_storage_controller_forward_404: release-arm64-with-lfc
• test_scrubber_physical_gc_timeline_deletion: release-arm64-with-lfc

Postgres 16

• test_hot_standby_gc[True]: release-x86-64-with-lfc
• test_ps_unavailable_after_delete[DeletionAPIKind.FORCE]: release-x86-64-with-lfc

Postgres 15

• test_hot_standby_gc[True]: release-x86-64-with-lfc
• test_lfc_prefetch: release-arm64-with-lfc
• test_ps_unavailable_after_delete[DeletionAPIKind.FORCE]: release-x86-64-with-lfc

Postgres 14

• test_ps_unavailable_after_delete[DeletionAPIKind.FORCE]: release-x86-64-with-lfc

Code coverage* (full report)

• functions: 34.7% (8804 of 25340 functions)
• lines: 45.8% (71298 of 155614 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
915229b at 2025-07-24T10:38:00.632Z :recycle:}

[tristan957]

I personally would like to see this move into its own extension. neon extension should just become what is necessary to enable serverless Postgres. No need to do any changes yet unless we can all agree.