### What changes were proposed in this pull request?
Update infrastructure for SSL support.
Please see #2416 for the consolidated PR with all the changes for reference.
### Why are the changes needed?
At a high level, the changes are:
* `ManagedBuffer.convertToNettyForSsl`, to support SSL encryption.
* Add `EncryptedMessageWithHeader`, which is used to wrap the message and body, for use with SSL.
* `SslMessageEncoder` is an encoder for SSL
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
The overall PR #2416 (and this PR as well) passes all tests, and this PR includes relevant subset of tests.
Closes#2427 from mridulm/update-infra-for-ssl.
Authored-by: Mridul Muralidharan <mridulatgmail.com>
Signed-off-by: SteNicholas <programgeek@163.com>
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