gplay device-tiers (device-targeting for tiered delivery)

gplay device-tiers manages device tier configs, the app-scoped configuration that drives tiered content delivery: which devices fall into which tier, so Play can serve different assets to high-end and low-end devices. Shared conventions (auth, output, exit codes, --dry-run, --package pinning) are in gplay-cli-usage. The whole namespace is [experimental].

A config bundles three things (all expressed in the JSON body):

• device groups, named sets of device selectors (over RAM, device IDs, SoCs, system features),
• an ordered device tier set, tiers by descending priority,
• user country sets.

Immutable: create / get / list only