Add pgAdmin blueprint with Docker Compose and metadata

- Introduced pgAdmin entry in meta.json with relevant details and links.
- Added Docker Compose configuration for pgAdmin service.
- Included pgAdmin logo and template.toml for configuration settings.

blueprints/pgadmin/template.toml

@@ -0,0 +1,22 @@
+[variables]
+main_domain = "${domain}"
+admin_email = "${email}"
+admin_password = "${password:16}"
+
+[config]
+[[config.domains]]
+serviceName = "pgadmin"
+port = 80
+host = "${main_domain}"
+
+[config.env]
+PGADMIN_DEFAULT_EMAIL = "${admin_email}"
+PGADMIN_DEFAULT_PASSWORD = "${admin_password}"
+
+[[config.mounts]]
+filePath = "/var/lib/pgadmin/servers.json"
+content = """
+{
+    "Servers": {}
+}
+"""