Metrics miss `op` configured

I forgot to set op: op, and thus we have metrics that:

• decrease counter on a proper op
• increase counter on a ""

Examples:

• https://prometheus-app.gprd.gitlab.net/graph?g0.range_input=1h&g0.expr=sum(gitlab_pages_zip_cached_entries)%20by%20(op%2Ccache)&g0.tab=1
• https://prometheus-app.gprd.gitlab.net/graph?g0.range_input=1h&g0.expr=sum(gitlab_pages_zip_cache_requests)%20by%20(op%2Ccache)&g0.tab=1