[Postgres] Add Postgres C++ library. Postgres can be used as a multi-…

…user replacement for our SQLite database, and it also could be used as a JSON database for the PatchInterchange format?

.gitmodules

@@ -48,3 +48,6 @@
 [submodule "third_party/spdlog"]
 	path = third_party/spdlog
 	url = https://github.com/gabime/spdlog.git
+[submodule "third_party/libpqxx"]
+	path = third_party/libpqxx
+	url = https://github.com/jtv/libpqxx.git

CMakeLists.txt

@@ -81,6 +81,14 @@ IF (WIN32)
 		include_directories("${asiosdk_SOURCE_DIR}/common")
 	ENDIF()
 
+	FetchContent_Declare(
+		postgresql
+		# Download the PostgreSQL 16.3 binaries from the official distributor. We need only the include and the library actually, need to look for a smaller distribution
+		URL https://sbp.enterprisedb.com/getfile.jsp?fileid=1259104
+	)
+	FetchContent_MakeAvailable(postgresql)
+	message("${postgresql_SOURCE_DIR} is the location for the postgres libraries")
+
 	FetchContent_Declare(
 		pythonembedded
 		URL https://www.python.org/ftp/python/${PYTHON_VERSION_TO_DOWNLOAD}/python-${PYTHON_VERSION_TO_DOWNLOAD}-embed-amd64.zip
@@ -228,6 +236,19 @@ add_subdirectory(third_party/fmt)
 option(SPDLOG_FMT_EXTERNAL "" ON)
 add_subdirectory(third_party/spdlog)
 
+# Add PostgreSQL
+set(PostgreSQL_LIBRARY "${postgresql_SOURCE_DIR}/lib" CACHE STRING "Lib directory for the Postgres SQL server")
+set(PostgreSQL_INCLUDE_DIR "${postgresql_SOURCE_DIR}/include" CACHE STRING "Include directory for the libpq C library for Postgres")
+set(PostgreSQL_TYPE_INCLUDE_DIR "${postgresql_SOURCE_DIR}/include" CACHE STRING "Type include directory for Postgres")
+message("${PostgreSQL_INCLUDE_DIR} is the include dir")
+set(SKIP_BUILD_TEST ON)
+IF (WIN32)
+    set(BUILD_SHARED_LIBS ON)
+ELSE()
+    set(BUILD_SHARED_LIBS OFF)
+ENDIF()
+add_subdirectory(third_party/libpqxx build-pqxx)
+
 # Import MidiKraft infrastructure 
 add_subdirectory(juce-utils)
 add_subdirectory(juce-widgets)