build(deps): update capnp requirement from 0.14.0 to 0.15.0 in /gst-depth-meta-rs

Updates the requirements on capnp to permit the latest version.

Commits

• 76ff980 prepare for 0.15.0 release
• 588aba0 Update Owned and OwnedStruct traits to use generic associated types
• 55476e6 update version number in comment
• db5c363 update some highlighting on old blog post
• 8458711 add test
• c903c4d wait for resolution
• 9893d29 fill in impl of get_local_server
• 51c5212 use local::Client::get_ptr()
• 0741f81 work in progress on CapabilityServerSet
• 27b3650 add ClientHook.as_client_hook()
• Additional commits viewable in compare view