Use efficient cache lifetimes

[coliff]

Right now static assets are set to be cached by browser for only 10 minutes. We should change to 1 year. It will improve performance for repeat visitors. It can be defined in netlify.toml config in root.

REF: https://developer.chrome.com/docs/performance/insights/cache?utm_source=lighthouse&utm_medium=devtools

[martinheidegger]

Right now the oktech.jp site is hosted on github pages still.