Configure zstd as default bucket encoding.

[Dav1dde]

We currently support different encodings per namespace via global config, we should remove the global config options and use zstd by default for all namespaces.

• Remove global config options from Sentry
• Use zstd for all namespaces in Relay

[jan-auer]

I would suggest to set the defaults to what we have now configured in production:

• zstd for distributions
• base64 for sets. There have been cases we measured where zstd made things worse in sets.