Option to use hex string as secret key

[ZTHawk]

I have added an option (checkbox + msg.isSecretKeyHex (bool)) to interpret the secret key as a hex string.
This allows to use byte arrays to be used as a key (byte array as hex string).

This also contains the pull request by @kongkrit.

[ZTHawk]

This is an old request, but I am using those changes frequently.
Will you ever merge the pull request?

[vivekrp]

Hey @ZTHawk, sorry for the delayed response. I hadn't reviewed this PR earlier. I initially created this package for personal use when I was working with NodeRED a while ago. The original package lacked a feature I needed, so I forked it and added that functionality when the original creator was inactive. Recently, I noticed on the npmjs website that thousands of users are downloading this package, so I came to check and saw this PR. I didn't realize so many people were using it. Will the changes you're proposing break any existing functionality of this package? I haven't worked on NodeRED for almost 2 years now, so I'm unsure of the recent changes.

[ZTHawk]

Hi, There is a breaking change from the merge 94b51bc ("secrectkey" to "secretkey").
This should affect users that are passing the secret key with msg. I am not sure what happens if key is written in the UI and then the module is updated.

Other than that, it is behaving the same way.
You can also decide to implement it your way. All I need is the feature to have the key to be interpreted as a hex (binary) key.