Add missing max-age cache directive

[ulrikandersen]

Adds the max-age directive to the cache control header which is going to tell the browser for how long it should cache the image for.

Max age is set to 1 hour to allow us to change images without waiting for 30 days for users' browser caches to expire.

[simonbs]

@ulrikandersen Do you know how this will work? Will the image still be cached beyond one hour in which case the browser shows a stale image while revalidating or does it only apply the SWR logic within that hour?

I'm thinking we could cache icons basically infinitely as long as we refresh the image while showing a stale image.

[ulrikandersen]

@ulrikandersen Do you know how this will work? Will the image still be cached beyond one hour in which case the browser shows a stale image while revalidating or does it only apply the SWR logic within that hour?

I'm thinking we could cache icons basically infinitely as long as we refresh the image while showing a stale image.

I am actually not sure how widely supported the stale-while-revalidate header is 🤔 Can I Use?
Perhaps it is mainly something supported by Next's SWR and not for normal browser requests. If this is tru we should only use max-age and choose it according to how long we can accept an old image to be shown. Alternatively we could look into making the image name change when the actual image changes in the repo.

[simonbs]

Alternatively we could look into making the image name change when the actual image changes in the repo.

I think we can quite easily do this, especially if query parameters in a URL are taken into consideration when browsers cache images, but I suppose they are.

I'm pretty sure we can get the ID of the commit in which a file was updated through the one request we do to GraphQL. If that's the case then we can just add that as a query parameter to the URL we use for loading the image. That way the URL will change when a new commit is made.

[simonbs]

With the changes in #115 the image URLs will change for every commit to a branch.

@ulrikandersen #115 targets this PR so we can test it out if you think this will allow us to cache images more reliably.

[ulrikandersen]

With image URLs changing when files change we are safe to instruct browser to cache for a long time (30 days).

I have removed stale-while-revalidate as it will have no effect (and most browsers don't support it).