Disable the replication adapters that are not actively maintained

[reasonerjt]

Replication adapters were introduced to support replication between Harbor and other registries and there's a long list of them:
https://github.com/goharbor/harbor/wiki/Harbor-Replicaiton-Adapter-Owner

Some of these adapters were contributed by community developers but are not actively maintained.

Before we can deprecate and remove them from main branch, as a short-term workaround, we should introduce an env var like "DISABLED_REPLICATION_ADAPTERS" to hide some of these adapters. Downstream vendors of Harbor can use this list to hide the replication adapters that they are not able to support.