Prepare pg 15 support (build system and submodules) (#2337)

* Add submodule postgres-15

* Support pg_15 in pgxn/neon

* Renamed zenith -> neon in Makefile

* fix name of codestyle check

* Refactor build system to prepare for building multiple Postgres versions.

Rename "vendor/postgres" to "vendor/postgres-v14"

Change Postgres build and install directory paths to be version-specific:

- tmp_install/build -> pg_install/build/14
- tmp_install/* -> pg_install/14/*

And Makefile targets:

- "make postgres" -> "make postgres-v14"
- "make postgres-headers" -> "make postgres-v14-headers"
- etc.

Add Makefile aliases:

- "make postgres" to build "postgres-v14" and in future, "postgres-v15"
- similarly for "make postgres-headers"

Fix POSTGRES_DISTRIB_DIR path in pytest scripts

* Make postgres version a variable in codestyle workflow

* Support vendor/postgres-v15 in codestyle check workflow

* Support postgres-v15 building in Makefile

* fix pg version in Dockerfile.compute-node

* fix kaniko path

* Build neon extensions in version-specific directories

* fix obsolete mentions of vendor/postgres

* use vendor/postgres-v14 in Dockerfile.compute-node.legacy

* Use PG_VERSION_NUM to gate dependencies in inmem_smgr.c

* Use versioned ECR repositories and image names for compute-node.
The image name format is compute-node-vXX, where XX is postgres major version number.
For now only v14 is supported.
Old format unversioned name (compute-node) is left, because cloud repo depends on it.

* update vendor/postgres submodule url (zenith->neondatabase rename)

* Fix postgres path in python tests after rebase

* fix path in regress test

* Use separate dockerfiles to build compute-node:
Dockerfile.compute-node-v15 should be identical to Dockerfile.compute-node-v14 except for the version number.
This is a hack, because Kaniko doesn't support build ARGs properly

* bump vendor/postgres-v14 and vendor/postgres-v15

* Don't use Kaniko cache for v14 and v15 compute-node images

* Build compute-node images for different versions in different jobs

Co-authored-by: Heikki Linnakangas <heikki@neon.tech>

.github/workflows/codestyle.yml

@@ -27,8 +27,10 @@ jobs:
         # Rust toolchains (e.g. nightly or 1.37.0), add them here.
         rust_toolchain: [1.58]
         os: [ubuntu-latest, macos-latest]
+        # To support several Postgres versions, add them here.
+        postgres_version: [v14, v15]
     timeout-minutes: 60
-    name: run regression test suite
+    name: check codestyle rust and postgres
     runs-on: ${{ matrix.os }}
 
     steps:
@@ -61,14 +63,14 @@ jobs:
 
       - name: Set pg revision for caching
         id: pg_ver
-        run: echo ::set-output name=pg_rev::$(git rev-parse HEAD:vendor/postgres)
+        run: echo ::set-output name=pg_rev::$(git rev-parse HEAD:vendor/postgres-${{matrix.postgres_version}})
 
-      - name: Cache postgres build
+      - name: Cache postgres ${{matrix.postgres_version}} build
         id: cache_pg
         uses: actions/cache@v3
         with:
           path: |
-            tmp_install/
+            pg_install/${{matrix.postgres_version}}
           key: ${{ runner.os }}-pg-${{ steps.pg_ver.outputs.pg_rev }}
 
       - name: Set extra env for macOS
@@ -90,10 +92,10 @@ jobs:
         if: failure()
         continue-on-error: true
         run: |
-          echo '' && echo '=== config.log ===' && echo ''
-          cat tmp_install/build/config.log
-          echo '' && echo '=== configure.log ===' && echo ''
-          cat tmp_install/build/configure.log
+          echo '' && echo '=== Postgres ${{matrix.postgres_version}} config.log ===' && echo ''
+          cat pg_install/build/${{matrix.postgres_version}}/config.log
+          echo '' && echo '=== Postgres ${{matrix.postgres_version}} configure.log ===' && echo ''
+          cat pg_install/build/${{matrix.postgres_version}}/configure.log
 
       - name: Cache cargo deps
         id: cache_cargo