Hide zenoh_config internals

[fuzzypixelz]

Addresses #1417 and #1304 with the following changes:

• Replace zenoh::Config with zenoh::config::Config leaving zenoh_config::Config unchanged.
• Add a new zenoh_config::Config with the following public items:
  • Default, Debug, Clone and Default impls
  • Deref<Target = InternalConfig> and DerefMut<Target = InternalConfig> impls with cfg(feature = "unstable_config")]
  • from_env, from_file, insert_json5, get and remove
• Reduce zenoh::config to the following public items:
  • Config
  • InsertionError
  • LookupError
  • LookupGuard
  • WhatAmI (for zenoh::scout)
  • WhatAmIMatcher (for zenoh::scout)
  • Notifier (for zenoh::Session::config)
  • Notification (for zenoh::config::Notifier)
• Move Notifier to the zenoh crate with the following API:
  • new (not sure about this one)
  • subscribe
  • notify
  • lock
  • remove
  • insert_json5
  • get

Older code using the zenoh_config::Config API will still compile provided that items such as ModeDependentValue are imported from zenoh_config.

---

I believe the Config API changes is ready to be propagated to bindings. Here are CI runs to know what's going wrong:

• cc @wyfo https://github.com/eclipse-zenoh/zenoh-python/actions/runs/10886444693/job/30245908828
• cc @sashacmc https://github.com/eclipse-zenoh/zenoh-c/actions/runs/10886423431/job/30245904074
• cc @DariusIMP https://github.com/eclipse-zenoh/zenoh-java/actions/runs/10899780569
• cc @DariusIMP https://github.com/eclipse-zenoh/zenoh-kotlin/actions/runs/10886495298