MINIFICPP-2282 Support re-encryption of sensitive properties

[fgerlits]

Added a new --re-encrypt option to the flow-config action of the encrypt-config binary, which can decrypt the sensitive properties using the .old key and re-encrypt them with a new key (either supported by the user or auto-generated).

https://issues.apache.org/jira/browse/MINIFICPP-2282

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[fgerlits]

There is a problem with this pull request: if you run encrypt-config flow-config --re-encrypt twice, then it encrypts the already-encrypted properties a second time, making them unusable. I'll put the PR in draft mode until I fix this.

Update: fixed in 7fd97273f2eb5798777fc3a0e2b7e359d8758427