file cache should be able to create directories

[trashhalo]

if you put a / in your cache key today file cache errors ERRO failed to write result to cache: %!s(<nil>) @service=redpanda-connect label="" path=root.pipeline.processors.0.branch.processors.0. It would be helpful if it did not error because then file could mimic object stores like s3 for local development.

[trashhalo]

I also tried:

cache_resources:
  - label: file_cache
    file:
      directory: /cache/${! meta("X-Tenant-Id") }

but that had the same error.