Add support for new encrypted expression resources

Support pluggable expression resolvers. Support an expression resolver backed by a credential store.

This would be the new recommended capability to store and secure configuration strings for users who are used to using old vault to mask (secure) other string than passwords (e.g. usernames, file paths, urls, …​)

The implementation will not be storing the encrypted values within the credential store as that is a store of credentials and not a generic store of strings, instead the encrypted values will be stored in the management model in-line as an expression. A configured expression resolver will then handle the decryption of these expressions using a specific key stored within the CredentialStore.

Add support in the console for the following new Elytron resources:

New tests will be added to the test suite to test the new resources.

See the official HAL website at https://hal.github.io