Pre create anon ext

[lubennikovaav]

Problem

It is not possible to create anon extension, because it requires superuser to install the extension:

From extension docs:

pg_catalog is always owned by the initial superuser role.
So in practice, you need to be superuser to run the SECURITY LABEL command, 
which means that you need to be superuser to install the extension.

https://gitlab.com/dalibo/postgresql_anonymizer/-/blob/master/anon.sql#L30

--
-- By default, masking filter functions must be trusted
-- and we only trust functions from `pg_catalog` and `anon` namespaces
-- This can be bypassed by setting `anon.restrict_to_trusted_schemas` to false
--
SECURITY LABEL FOR anon ON SCHEMA pg_catalog IS 'TRUSTED';

Summary of changes

• Add anon extension to compute image.

• If anon is in shared_preload_libraries and feature flag anon_extension is set in control-plane,
  pre-create extension from superuser at compute start. Run anon.init() and adjust grants to allow db_owner to use the extension.

• Some functions in anon.sql that access these GUCs are SECURITY DEFINER (called with owner privileges).
  So, I change their ownership to db_owner. As well as ownership of other objects in the schema.

Since we don't have any good concept of superuser yet, I decided that db_owner is a good candidate for "superuser-like" role in the context of anon extension.

• To allow db_owner to start and stop dynamic masking, I had to patch anon extension
  This PR uses neon fork of postgresql_anonymizer

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I've tested it in preview with commands from this script.
https://gist.github.com/lubennikovaav/33e3fe1acafed9be452fc32261683dad

[github-actions]

2394 tests run: 2278 passed, 0 failed, 116 skipped (full report)

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Flaky tests (3)

Postgres 15

• test_timeline_deletion_with_files_stuck_in_upload_queue: release

Postgres 14

• test_empty_branch_remote_storage_upload: debug
• test_empty_tenant_size: debug

Code coverage (full report)

• functions: 54.1% (11287 of 20861 functions)
• lines: 81.2% (63479 of 78167 lines)

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_{The comment gets automatically updated with the latest test results
d97db42 at 2024-02-08T11:18:13.381Z :recycle:}

[knizhnik]

Should we first merge neondatabase/postgres#339 (na similar PRs for other Postgres versions) before enabling anon. Because as far as I understand without this patch anon extension still can not be used for Neon users.