feat(ofi): Require asiofi 0.5

* Modernize some ofi transport code along the way
  * Replace Boost.Container with `<memory_resource>`
  * Introduce namespaced headers
    * `<fairmq/Channel.h>`
    * `<fairmq/Message.h>`
    * `<fairmq/Poller.h>`
    * `<fairmq/Socket.h>`
    * `<fairmq/TransportFactory.h>`
    * `<fairmq/UnmanagedRegion.h>`
* Compile-firewall Boost.Process in `shmem::Manager` because it conflicts
with standalone asio

fairmq/shmem/Manager.cxx

@@ -0,0 +1,48 @@
+/********************************************************************************
+ *    Copyright (C) 2021 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH    *
+ *                                                                              *
+ *              This software is distributed under the terms of the             *
+ *              GNU Lesser General Public Licence (LGPL) version 3,             *
+ *                  copied verbatim in the file "LICENSE"                       *
+ ********************************************************************************/
+
+#include "Manager.h"
+
+// Needed to compile-firewall the <boost/process/async.hpp> header because it
+// interferes with the <asio/buffer.hpp> header. So, let's factor
+// the whole dependency to Boost.Process out of the header.
+#include <boost/process.hpp>
+#include <fairlogger/Logger.h>
+
+namespace fair::mq::shmem {
+
+bool Manager::SpawnShmMonitor(const std::string& id)
+{
+    auto const env(boost::this_process::environment());
+    std::string const fairmq_path_key("FAIRMQ_PATH");
+    std::string const shmmonitor_exe_name("fairmq-shmmonitor");
+    std::string const shmmonitor_verbose_key("FAIRMQ_SHMMONITOR_VERBOSE");
+    auto path(boost::this_process::path());
+
+    if (env.count(fairmq_path_key)) {
+        path.emplace(path.begin(), env.at(fairmq_path_key).to_string());
+    }
+
+    auto exe(boost::process::search_path(shmmonitor_exe_name, path));
+    if (exe.empty()) {
+        LOG(warn) << "could not find " << shmmonitor_exe_name << " in \"$" << fairmq_path_key
+                  << ":$PATH\"";
+        return false;
+    }
+
+    // TODO Move this to fairmq-shmmonitor itself ?
+    bool verbose(env.count(shmmonitor_verbose_key)
+                 && env.at(shmmonitor_verbose_key).to_string() == "true");
+
+    boost::process::spawn(
+        exe, "-x", "-m", "--shmid", id, "-d", "-t", "2000", (verbose ? "--verbose" : ""), env);
+
+    return true;
+}
+
+}   // namespace fair::mq::shmem