Redirect outdated /contribute pages (Fixes #6994)

[alexgibson]

Description

• Redirect /contribute/signup/ and sub pages to https://activate.mozilla.community/
• Redirect /contribute/studentambassadors/ to https://campus.mozilla.community/
• Redirect /contribute/friends/ to /contribute/
• Update internal links to /contribute/signup/ to https://activate.mozilla.community/

Issue / Bugzilla link

#6994

Testing

• Check I didn't miss any stray unused assets?
• Check internal links to /signup are all updated?

Successful test run: https://ci.vpn1.moz.works/blue/organizations/jenkins/bedrock_multibranch_pipeline/detail/run-integration-tests/302/pipeline

[craigcook]

This all looks good, but it needs a rebase (just static-bundles.json, really). Though it's still marked as a draft so was there something else you needed to do? If not then feel free to merge after you rebase. r+ 📐

[alexgibson]

Rebased 🎉