Introduce `<sha512-hash>` tag compatibility in root password object

[mwood77]

User login creds support the following password hashing algorithms:

• bcrypt-hash (default)
• sha512-hash (optional)
• md5-hash (legacy)

sha512-hash was missing, and this PR introduces this.

Relevant references:

• https://redmine.pfsense.org/issues/12855
• https://redmine.pfsense.org/issues/6332
• https://github.com/pfsense/FreeBSD-ports/blob/22705d90d9b8164fa968f25a042839329daa868b/sysutils/pfSense-pkg-System_Patches/files/usr/local/pkg/patches/8ddf2b5a999772754080825f07acf9b6326f1f04.patch#L10C49-L11C1

Relevant issues:

7 #9