This commits reworks how file caching is performed in Hugo. Now there is only one way, and it can be configured.
This is the default configuration:
```toml
[caches]
[caches.getjson]
dir = ":cacheDir"
maxAge = -1
[caches.getcsv]
dir = ":cacheDir"
maxAge = -1
[caches.images]
dir = ":resourceDir/_gen"
maxAge = -1
[caches.assets]
dir = ":resourceDir/_gen"
maxAge = -1
```
You can override any of these cache setting in your own `config.toml`.
The placeholders explained:
`:cacheDir`: This is the value of the `cacheDir` config option if set (can also be set via OS env variable `HUGO_CACHEDIR`). It will fall back to `/opt/build/cache/hugo_cache/` on Netlify, or a `hugo_cache` directory below the OS temp dir for the others.
`:resourceDir`: This is the value of the `resourceDir` config option.
`maxAge` is the time in seconds before a cache entry will be evicted, -1 means forever and 0 effectively turns that particular cache off.
This means that if you run your builds on Netlify, all caches configured with `:cacheDir` will be saved and restored on the next build. For other CI vendors, please read their documentation. For an CircleCI example, see 6c3960a8f4/.circleci/config.ymlFixes#5404
In Hugo 0.46 we made the output of what you get from resources.Get and similar static, i.e. language agnostic. This makes total sense, as it is wasteful and time-consuming to do SASS/SCSS/PostCSS processing for lots of languages when the output is lots of duplicates with different filenames.
But since we now output the result once only, this had a negative side effect for multihost setups: We publish the resource once only to the root folder (i.e. not to the language "domain folder").
This commit removes the language code from the processed image keys. This creates less duplication in the file cache, but it means that you should do a `hugo --gc` to clean up stale files.
Fixes#5058
