vault-secret: Get key from Bitwarden

I don't use GnuPG for anything else anymore, so it's becoming rather
cumbersome to keep setting it up just for the Ansible Vault secret.
Since I use Bitwarden to store the passphrase for my PGP key anyway, it
makes sense to just store the Ansible Vault secret there directly.

.vault-secret.sh

@@ -1,2 +1,3 @@
 #!/bin/sh
-exec gpg --quiet --batch --decrypt "${0%.sh}.gpg"
+
+rbw get --folder Pyrocufflink 'Ansible Vault Key' | base64 -d