Refactor terms `blacklist` and `whitelist` to `denylist` and `allowlist`

[jfb]

There is an open feature request here:

Change blacklist and whitelist terminology

Like the UK NCSC says the terminology of blacklists and whitelists suggests black is associated with 'forbidden' and other negativity. I propose Pi-hole terminology Blacklist and Whitelist is changed to e.g. Denylist and Allowlist or Blocklist and Allowlist.