security/acme-client: DNS-01 nsupdate: Help for secret key should mention format

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Is your feature request related to a problem? Please describe.
It was unclear for me what to enter in the text field "Secret Key" for the challenge type "DNS-01", DNS Service "nsupdate (RFC 2136)". The help text currently says:

Requires the whole key file in a format that is compatible with nsupdate.

I entered the content of the key file as produced by tsig-keygen resp. dnssec-keygen:

Private-key-format: v1.3
Algorithm: 165 (HMAC_SHA512)
Key: 7DXXX...
Bits: AAA=
Created: 20240205213656
Publish: 20240205213656
Activate: 20240205213656

...which did not work.

After lengthy researches I found that the form, which is used in named.conf to define keys, did work:

key "_acme-challenge.example.com." {
  algorithm hmac-sha512;
  secret "7DXXX...";
};

The help text did not help me much. That's why I am asking to change it.

I don't know whether the code could work with the contents of a key file from tsig-keygen (I think it would need the pair of files K<xxx>.key and K<xxx>.private), if yes, then this request to change the help text is almost obsolete and there should be some testing with that key file format or describe how to use it.

Describe the solution you'd like
Since nsupdate supports two formats for key files, the help text is not wrong, but could be more elaborate to help. Please change the help text to say content of the key file, not to confuse with a path to a key file. Secondly, for as long as it is unclear whether the key file format from tsig-keygen does work or not, mention the format that works:

Enter the the key exactly as it is defined in named.conf of your bind server configuration, use the whole key{}-statement.

Please change this if needed, I am not a native speaker.

Describe alternatives you've considered
Alternatively:
Requires the whole content of the key file in a format that is compatible with nsupdate, which is one of two formats: a single key statement as used in named.conf of the bind server software, which was generated by ddns-confgen; or the content of the key file generated by dnssec-keygen resp. tsig-keygen.

Additional context
It might be possible that even SIG(0) key pairs are supported. In this case the help text should mention this as well.