fix(gcp): cache volatile content for 1h

[LeoMcA]

disable cdn invalidation by default in the build - it doesn't really
work in gcp: even after waiting the ~20 minutes it takes to "finish",
content is still cached for certain users in certain geos - but keep
the option for manual use in exceptional circumstances

Summary

https://mozilla-hub.atlassian.net/browse/MP-440

Problem

• cdn invalidation doesn't work well (or at all) in gcp

Solution

• stop using invalidation, set caching header to 1h on volatile content (i.e. content which doesn't have a hash in its path)

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How did you test this change?

I haven't yet, and I need help learning how :)
@caugner we'll peer review/test this tomorrow

[LeoMcA]

I also couldn't fully figure out what this cache header set, or if it was relevant at all - to discuss tomorrow:

yari/.github/workflows/prod-build.yml

Line 298 in 6f031fe

gsutil -q -m -h "Cache-Control: public, max-age=86400" cp -r client/build/static gs://${{ vars.GCP_BUCKET_NAME }}/main/