Support for [deployment] stanza pass4SymmKey

[DevAlphaKilo]

There is currently not support for the following configurations via environment variables according to the available documentation.

[deployment]
pass4SymmKey = some-secret

There is currently support for most pass4SymmKey key values for each allowed stanza but [deployment] is missing.

This environment variable should work exactly the same as any other not [general] pass4SymmKey key-value pairs.

Adding this support would be best practice to avoid having to use the [general] pass4SymmKey key on Deployment Server containers.

Link used: https://splunk.github.io/splunk-ansible/ADVANCED.html#inventory-script

[DevAlphaKilo]

Partially related to splunk/splunk-ansible#686