LMDB encryption is not supported through kong.conf

From Slack:

> On this [page](https://developer.konghq.com/gateway/hybrid-mode/#data-plane-cache-configuration) we have "If encrypted, the Data Plane uses the cluster certificate key to decrypt the LMDB database on startup."
I believe doing this through Kong ( declarative_config_encryption_mode) is no longer supported & has to be done by the underlying infra (e.g disk encryption).

We [removed support for LMDB encryption in 3.4](https://developer.konghq.com/gateway/changelog/#3-4-0-0-breaking-change):

> LMDB encryption has been disabled. The option declarative_config_encryption_mode has been removed from kong.conf.

We need to remove all references to encrypting the lmbd from https://developer.konghq.com/gateway/hybrid-mode/#data-plane-cache-configuration, and any other places if they exist.

Need to double check if there's some other way to encrypt it, now that the kong-native method isn't available, or if we don't want to tell people to do that.

Start with the Data Plane cache configuration section at the hybrid-mode documentation URL and compare its encryption guidance with the 3.4.0.0 breaking-change entry. Search the documentation for other references to LMDB encryption or declarative_config_encryption_mode, then confirm what guidance remains valid. Done means outdated Kong-native encryption references are removed or corrected without suggesting an unsupported approach.

Written by the indexing model from the issue text.