Tar Remote Extensions (#4715)

Add infrastructure to dynamically load postgres extensions and shared libraries from remote extension storage.

Before postgres start downloads list of available remote extensions and libraries, and also downloads 'shared_preload_libraries'. After postgres is running, 'compute_ctl' listens for HTTP requests to load files.

Postgres has new GUC 'extension_server_port' to specify port on which 'compute_ctl' listens for requests.

When PostgreSQL requests a file, 'compute_ctl' downloads it.

See more details about feature design and remote extension storage layout in docs/rfcs/024-extension-loading.md

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Co-authored-by: Anastasia Lubennikova <anastasia@neon.tech>
Co-authored-by: Alek Westover <alek.westover@gmail.com>

test_runner/regress/data/extension_test/5670669815/v14/ext_index.json

@@ -0,0 +1,24 @@
+{
+    "public_extensions": [
+        "anon",
+        "pg_buffercache"
+    ],
+    "library_index": {
+        "anon": "anon",
+        "pg_buffercache": "pg_buffercache"
+    },
+    "extension_data": {
+        "pg_buffercache": {
+            "control_data": {
+                "pg_buffercache.control": "# pg_buffercache extension \ncomment = 'examine the shared buffer cache' \ndefault_version = '1.3' \nmodule_pathname = '$libdir/pg_buffercache' \nrelocatable = true \ntrusted=true"
+            },
+            "archive_path": "5670669815/v14/extensions/pg_buffercache.tar.zst"
+        },
+        "anon": {
+            "control_data": {
+                "anon.control": "# PostgreSQL Anonymizer (anon) extension \ncomment = 'Data anonymization tools' \ndefault_version = '1.1.0' \ndirectory='extension/anon' \nrelocatable = false \nrequires = 'pgcrypto' \nsuperuser = false \nmodule_pathname = '$libdir/anon' \ntrusted = true \n"
+            },
+            "archive_path": "5670669815/v14/extensions/anon.tar.zst"
+        }
+    }
+}

test_runner/regress/data/extension_test/5670669815/v15/ext_index.json

@@ -0,0 +1,17 @@
+{
+    "public_extensions": [
+        "anon"
+    ],
+    "library_index": {
+        "anon": "anon"
+    },
+    "extension_data": {
+        "anon": {
+            "control_data": {
+                "anon.control": "# PostgreSQL Anonymizer (anon) extension \ncomment = 'Data anonymization tools' \ndefault_version = '1.1.0' \ndirectory='extension/anon' \nrelocatable = false \nrequires = 'pgcrypto' \nsuperuser = false \nmodule_pathname = '$libdir/anon' \ntrusted = true \n"
+            },
+            "archive_path": "5670669815/v15/extensions/anon.tar.zst"
+        }
+    }
+}
+