runtime-v2: add EL function to mark strings as sensitive

[ibodrov]

The EL function sensitive allows users to add any string to SensitiveDataHolder. Useful when sensitive strings are created directly in flows.

[ibodrov]

On second thought, maybe mask is not a good name. Users might have expectations that the function will mask "sensitive" substrings in the supplied string. While the intent for us to provide a function to mark generated data as "sensitive". Perhaps it should be just sensitive("foo") instead?

[brig]

On second thought, maybe mask is not a good name. Users might have expectations that the function will mask "sensitive" substrings in the supplied string. While the intent for us to provide a function to mark generated data as "sensitive". Perhaps it should be just sensitive("foo") instead?

+1 sensitive("foo")