Add a resource for the SiteRouter application #60

cozystack/cozystack#3426 adds new application kind SiteRouter (apps.cozystack.io/v1alpha1, plural siterouters, release prefix site-router-). Provider has no codegen from schema, so it needs resource and data source written for it from packages/apps/site-router/values.schema.json. Top-level fields are tunnel, peer, remoteCIDRs, staticRoutes, bgp, resources, storageClass and cloudInitSeed. remoteCIDRs is capped at 16 items, and API also rejects a CIDR that overlaps cluster networks, provider gets that as admission error on apply. Keys starting with _ are platform-injected and should not be in provider schema at all.