Added code to allow saving the cache directory

[Omegaice]

I wanted to utilize the cache action but this action didn't expose the cache directory, so I updated it to mount the cache directory.

It can be further enhanced by any users if they use something like the following in their config.toml to store the generated images and assets in the cache directory as well. The other option would be to also expose the generated directory as part of this action.

[caches]
  [caches.assets]
    dir = ':cacheDir/:project/_gen'
    maxAge = -1
  [caches.getcsv]
    dir = ':cacheDir/:project'
    maxAge = -1
  [caches.getjson]
    dir = ':cacheDir/:project'
    maxAge = -1
  [caches.images]
    dir = ':cacheDir/:project/_gen'
    maxAge = -1
  [caches.modules]
    dir = ':cacheDir/modules'
    maxAge = -1