ECDS support

[hypnoce]

This issue focuses on ECDS (another issue was opened for ECDS and VHDS: #346).

ECDS uses TypeExtensionConfig as resource.
Leveraging the current server, caches and snapshots can help anyone implementing an ECDS, and also simplify the usage of an ADS server to serve extension configs.

I will provide a PR. Let me know if that's smth you would like implemented.