Use Equinix red in the top nav bar

[displague]

As seen in https://equinix-labs.github.io/terraform-on-equinix-workshop/, adopt the Equinix brand's red color for the top nav bar.

[ctreatma]

After some investigation, "Equinix red" is already configured in this repo and all workshops created from it, but it doesn't take effect on the live workshop pages for most repos. We need to update our configuration to match the documentation for using custom colors: https://squidfunk.github.io/mkdocs-material/setup/changing-the-colors/#custom-colors

[ocobles]

I opened this issue last year. The logs for the last repositories where it was still red have already expired, but I could verify that it was after the mkdocs version update 9.1.8 https://github.com/equinix-labs/eks-anywhere-on-equinix-metal-workshop/issues/5