[Feature] Add rspamadm secretbox command

[Feature] Add rspamadm secretbox command

* [Minor] Small fix for error messages

* [Feature] Create rspamadm util to decrypt header

* [Feature] Create python example to encrypt/decrypt header

* [Minor] Small clean up

* [Minor] Change c-rspamadm util to lua-rspamadm util

* [Minor] Small clean up

* [Minor] Add some debug

* [Feature] Add secretbox command

* [Minor] Debug

* [Minor] Add additional return for encrypted string(noce + encrypted string

* [Minor] Small debug

* [Minor] Add a way to provide encrypted text concatenated with nonce

* [Minor] Add nonce to encrypt text

* [Minor] Clean up

* [Minor] Clean up unused variable

* [Minor] Small fix

* [Minor] Fix return issue

* [Minor] Add blake2b for key derivation

* [Minor] Small upgrade to debug

* [Minor] Small clean up

* [Minor] Change return to more convenient form

* [Minor] Change print to test form

* [Test] Provide tests for encrypt/decrypt with rspamadm util and python script

* [Minor] Change python to python3

* [Minor] Add stderr check

* [Minor] Make the function return nonce+text

* [Minor] Change unit tests to new return format

* [Minor] Add flag to manage encodings

* [Minor] Add --encoding argument to manage encodings

* [Minor] Change tests for new input format

* [Minor] Fix lua format

* [Minor] Small fix

* [Minor] Provide full support for new return format of maybe_encrypt_header

* [Test] Test small fix

* [Test] Small fix

* [Minor] Clean up

* [Minor] Small fix for name of variable

* [Minor] Small clean up

* [Minor] Change format of command to a mre convenient

* [Minor] Change tests to be same as a format of a command

* [Minor] Change description of flags

* [Minor] Small fix

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Co-authored-by: Ivan Stakhov <50211739+LeftTry@users.noreply.github.com>