introduce autotools deprecation warning

Description

As autotools will be deprecated in the future, we are now printing a warning (with user confirmation) at the end of the configure script. This warning can be disabled with the --enable-silent_deprecation flag.

News snippet

Deprecate autotools.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

m4/octopus_compilation_info.m4

@@ -54,3 +54,13 @@ GIT_COMMIT=$hash
 AC_SUBST([GIT_COMMIT])
 ]
 )
+
+AC_DEFUN([ACX_PROMPT_USER],
+[
+echo ""
+echo "WARNING: AutoTools are deprecated and will be removed in future."
+echo "Please, use CMake instead. See cmake/README.md for more information."
+echo ""
+echo "Press any key to continue." >&AS_MESSAGE_FD
+read dummy <&AS_ORIGINAL_STDIN_FD
+])
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