[BUG] use of _customPathPrefix is creating links with additional /

[edhamiltonHO]

Describe the bug
In the phase banner the updated feedback link from #263 is https://ho-cto.github.io/engineering-guidance-and-standards//provide-feedback/

This is because that link is generated by concatenating the _customPathPrefix with /provide-feedback/

This is also happening in links in footer items, and the img source link for the organisation logo in the header. It may be happening in other areas and should be investigated.

Expected behavior
Links should not include additional /

Additional context
As the use of _customPathPrefix will likely change during migration to new hosting, this should be fixed as part of that process.