Announce the new core secretary PGP key

It is signed with the old core secretary key.

$ gpg --list-sigs 0xBE3DF7A86914D607
pub rsa4096/0xBE3DF7A86914D607 2022-07-29 [SC] [expires: 2024-07-28]

Key fingerprint = E0C0 73CF 01A2 A902 800C  3680 BE3D F7A8 6914 D607

uid [ultimate] FreeBSD Core Team Secretary <core-secretary@freebsd.org>
sig 3 0xBE3DF7A86914D607 2022-07-29 FreeBSD Core Team Secretary <core-secretary@freebsd.org>
sig 0xD8C8C83B49F26F17 2022-07-29 FreeBSD Core Team Secretary <core-secretary@freebsd.org>
sub rsa4096/0x7882C7A2CA320B52 2022-07-29 [E] [expires: 2024-07-28]
sig 0xBE3DF7A86914D607 2022-07-29 FreeBSD Core Team Secretary <core-secretary@freebsd.org>