Warn macOS Arm users who install the Intel package (#39872)

### Description of work
Warn macOS users who install an Intel build on an Arm machine.

Closes #39763 


### To test:
Install the package from this build:
x86: [![Build
Status](https://builds.mantidproject.org/job/build_packages_from_branch/1329/badge/icon)](https://builds.mantidproject.org/job/build_packages_from_branch/1329/)
ARM: [![Build
Status](https://builds.mantidproject.org/job/build_packages_from_branch/1331/badge/icon)](https://builds.mantidproject.org/job/build_packages_from_branch/1331/)
- on Arm macOS machine - check there is a warning
- on Intel macOS machine - check there is **no** warning.



---------

Co-authored-by: Caila Finn <47181718+cailafinn@users.noreply.github.com>

Author: thomashampson

Framework/Kernel/src/ConfigService.cpp

@@ -1026,6 +1026,9 @@ std::string ConfigServiceImpl::getOSArchitecture() {
     size_t size = sizeof(ret);
     if (sysctlbyname("sysctl.proc_translated", &ret, &size, nullptr, 0) != -1 && ret == 1) {
       osArch = "arm64_(x86_64)";
+      g_log.warning("You are running an Intel build of Mantid on Apple silicon, which will be significantly slower and "
+                    "use more power. For best performance, install the Arm version of Mantid. This version is "
+                    "available here: https://downloads.mantidproject.org");
     } else {
       // TODO this can be removed after the v6.14 code freeze because the feature will be dropped
       g_log.warning("Mantid v6.14 is the last version that will support Intel macOS.");

docs/source/release/v6.14.0/Framework/Python/New_features/39763.rst

@@ -0,0 +1 @@
+- macOS users with Apple silicon (Arm-based architecture) are now warned if they have installed the Intel-based Mantid package.