Add testing for extensions

[a-masterov]

Problem

We need automated tests of extensions shipped with Neon to detect possible problems.

Summary of changes

A new image neon-test-extensions is added. Workflow changes to test the shipped extensions are added as well.
Currently, the regression tests, shipped with extensions are in use.
Some extensions, i.e. rum, timescaledb, rdkit, postgis, pgx_ulid, pgtap, pg_tiktoken, pg_jsonschema, pg_graphql, kq_imcx, wal2json_2_5 are excluded due to problems or absence of internal tests.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

3222 tests run: 3080 passed, 0 failed, 142 skipped (full report)

---

Flaky tests (1)

Postgres 14

• test_storage_controller_smoke: debug

Code coverage* (full report)

• functions: 31.5% (6601 of 20962 functions)
• lines: 48.5% (51091 of 105428 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
3707327 at 2024-06-11T09:49:07.341Z :recycle:}

[bayandin]

Nice, let's merge it

[hlinnaka]

I think this broke the docker-compose script:

~/git-sandbox/neon/docker-compose$ PG_VERSION=16 docker-compose up --build -d
WARNING: The http_proxy variable is not set. Defaulting to a blank string.
WARNING: The https_proxy variable is not set. Defaulting to a blank string.
Building compute
Sending build context to Docker daemon  11.78kB
Step 1/9 : ARG REPOSITORY=neondatabase
Step 2/9 : ARG COMPUTE_IMAGE=compute-node-v14
Step 3/9 : ARG TAG=latest
Step 4/9 : FROM $REPOSITORY/${COMPUTE_IMAGE}:$TAG
 ---> 6e46b70231b9
Step 5/9 : USER root
 ---> Using cache
 ---> 3f0939567576
Step 6/9 : RUN apt-get update &&           apt-get install -y curl                        jq                          python3-pip                        netcat
 ---> Using cache
 ---> 22c5960a3904
Step 7/9 : RUN pip3 install Faker
 ---> Using cache
 ---> 68771ebf7dc8
Step 8/9 : RUN mkdir -p /ext-src/pg_hint_plan-src && chown postgres /ext-src/pg_hint_plan-src
 ---> Using cache
 ---> 09cb069f8789
Step 9/9 : USER postgres
 ---> Using cache
 ---> 77c11ff069bc
Successfully built 77c11ff069bc
Successfully tagged docker-compose_compute:latest
Pulling neon-test-extensions (neondatabase/neon-test-extensions-v16:latest)...
ERROR: manifest for neondatabase/neon-test-extensions-v16:latest not found: manifest unknown: manifest unknown