Allow ".esphome/platformio" storage location to be configured

[markormesher]

Describe the problem you have/What new integration you would like

PlatformIO packages, platforms and cache are currently stored in .esphome/platformio under the config folder. When running in a container this folder is usually mounted as a volume, meaning that volume grows considerably. On my very modest setup with about a dozen devices I have a few KB of YAML configs and C++ library files, and over 500MB of data under .esphome/platformio.

This is especially problematic when volumes are backed by block storage devices because backups operate at the block level, meaning we have to store over 500MB to backup a few KB of YAML.

Please describe your use case for this integration and alternatives you've tried:

I've already changed esphome.build_path to move build files to ephemeral storage which redirected a few 10s of MB out of the volume, but that's <10% of the storage usage picture.

Additional context