feat: add a --schema flag to dump the HCL schema

[alecthomas]

Current schema from running cachewd --schema

// The stable API of the cache server.
apiv1 {}

// Caches artifacts from an Artifactory server.
artifactory target {
  // List of hostnames to accept for host-based routing. If empty, uses path-based routing only.
  hosts = [string](optional)
}

// Caches objects on local disk, with a maximum size limit and LRU eviction
disk {
  // Root directory for the disk storage.
  root = string
  // Maximum size of the disk cache in megabytes (defaults to 10GB).
  limit-mb = number(optional default(10240))
  // Maximum time-to-live for entries in the disk cache (defaults to 1 hour).
  max-ttl = string(optional default("1h"))
  // Interval at which to check files for eviction (defaults to 1 minute).
  evict-interval = string(optional default("1m"))
}

// Caches Git repositories, including bundle and tarball snapshots.
git {
  // Directory to store git clones.
  mirror-root = string
  // How often to fetch from upstream in minutes.
  fetch-interval = string(optional default("15m"))
  // How long to cache ref checks.
  ref-check-interval = string(optional default("10s"))
  // How often to generate bundles. 0 disables bundling.
  bundle-interval = string(optional default("0"))
  // Depth for shallow clones. 0 means full clone.
  clone-depth = number(optional default(0))
}

// Caches public and authenticated GitHub releases.
github-releases {
  // GitHub token for authentication.
  token = string
  // List of private GitHub organisations.
  private-orgs = [string]
}

// A generic host-based proxying strategy.
host target {}

// Caches objects in memory, with a maximum size limit and LRU eviction
memory {
  // Maximum size of the disk cache in megabytes (defaults to 1GB).
  limit-mb = number(optional default(1024))
  // Maximum time-to-live for entries in the disk cache (defaults to 1 hour).
  max-ttl = string(optional default("1h"))
}

// Caches objects in S3
s3 {
  // S3 bucket name.
  bucket = string
  // S3 endpoint URL (e.g., s3.amazonaws.com or localhost:9000).
  endpoint = string(optional default("s3.amazonaws.com"))
  // S3 region (defaults to us-west-2).
  region = string(optional default("us-west-2"))
  // Use SSL for S3 connections (defaults to true).
  use-ssl = boolean(optional default(true))
  // Skip SSL certificate verification (defaults to false).
  skip-ssl-verify = boolean(optional default(false))
  // Maximum time-to-live for entries in the S3 cache (defaults to 1 hour).
  max-ttl = string(optional default("1h"))
  // Number of concurrent workers for multi-part uploads (0 = use all CPU cores, defaults to 1).
  upload-concurrency = number(optional default(1))
  // Size of each part for multi-part uploads in megabytes (defaults to 16MB, minimum 5MB).
  upload-part-size-mb = number(optional default(16))
}