CAMEL-20172: Add checksum feature to camel-file/ftp

[graben]

Hi @davsclaus, JIRA issue (CAMEL-20172) and PR as requested.

[github-actions]

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[orpiske]

LGTM, but I'd suggest moving the block of code to a separate method as we already have too many large blocks of code.

[zipwiz]

Too late, however: This produces a checksum file after completion of the "temp file mechanism", i. e. if use of "temp named" file is requested, then first the "temp named" file is transferred, then this file is renamed to its final name AND THEN the checksum file is generated and transferred WITH ITS FINAL NAME. This is not always useful: We have a requirement to (1) transfer file + checksum WITH TEMP NAME and (2) afterwards rename both files, the checksum file being the first to rename. Currently this is not feasible with this code. What about changing the impl to behave this way always? (or to make this requestable by a new parameter? There are myriads of parameters already anyway). I think that is not a too exotic feature.

[zipwiz]

Just one more thing: Would be KEWL to have the possibility to not only hash but digitally sign transferred files this way. The default private key + passphrase for signing could be the SSH private key given as a parameter for SFTP / FTPS / SCP anyway, completed by the encryption algo (like RSA or newer), of cource alternatively another private key + passphrase just for the purpose of signing ... (yes, I need this, and for the time being I will try to solve it with a custom Processor impl...)