Upadate the docs/tag.d for certificate_authority tag

[varsharain-a11y]

Update ### Tag - certificate_authority description here: https://github.com/confluentinc/cp-ansible/blob/41620d6b313a91b154e3f341b99bf8ff86658002/docs/TAGS.md?plain=1#L16

Tag - certificate_authority alongside creating self signed certificates also generates the MDS token key pair : private key and public certificate to be used in the MDS. ansible/blob/41620d6b313a91b154e3f341b99bf8ff86658002/playbooks/tasks/certificate_authority.yml#L118 "Description: To generate the certificate authority (CA) if TLS encryption is enabled and using self-signed certificates .Additionally, it will generate a key pair for the MDS token: a private key and a public certificate for use in the MDS. "