[feature]: Support for RFC 9887 - TACACS+ over TLS 1.3

[pgiralt]

What type of feature is needed?

Changed behavior to existing functionality

What is the feature?

TACACS+ over TCP uses MD5 for obfuscation of secrets on the network and the use of a weak algorithm presents a security risk in modern networks. RFC9887 addresses this problem by proposing a mechanism to transport TACACS+ traffic over a secure TLS 1.3 connection, eliminating the obfuscation mechanism defined in RFC8907.

FreeRADIUS should add support for RFC9887 by allowing users to authenticate a remote network device through the verification and authentication of the client certificate presented by the device as defined in the RFC.