Add link to OpenCL ARM sample to Antora navigation, update templates

[SaschaWillems]

Description

This PR adds the vendor-specific OpenCL ARM sample to the navigation for the Antora site so that it's documentation can be accessed from the docs site.

The PR also slightly adds a new entry to the the pull request template checklist for new samples:

For new samples, I have added a link to the Antora navigation so that the sample will be listed at the Vulkan documentation site

This is a pure documentation fix

General Checklist:

Please ensure the following points are checked:

• My code follows the coding style
• I have reviewed file licenses
• I have commented any added functions (in line with Doxygen)
• I have commented any code that could be hard to understand
• My changes do not add any new compiler warnings
• My changes do not add any new validation layer errors or warnings
• I have used existing framework/helper functions where possible
• My changes do not add any regressions
• I have tested every sample to ensure everything runs correctly
• This PR describes the scope and expected impact of the changes I am making

Note: The Samples CI runs a number of checks including:

• I have updated the header Copyright to reflect the current year (CI build will fail if Copyright is out of date)
• My changes build on Windows, Linux, macOS and Android. Otherwise I have documented any exceptions