SITE: test and fix command-related scripts

[dwdougherty]

This PR accomplishes a couple of things:

1. It updates the update_cmds.py and add_cmds.py scripts to account for changes to newly generated data/commands_core.json files.
2. It removes superfluous front matter from each command page; syntax_str was never used, even on the old site. Lots of changes here, but it's mostly the same for every command page.

[cmilesb]

Looks okay to me after a quick scan.

[dwdougherty]

Thank you @cmilesb!

[github-actions]

Staging links:
https://redis.io/docs/staging/DOC-6063/commands/acl-cat/
https://redis.io/docs/staging/DOC-6063/commands/acl-deluser/
https://redis.io/docs/staging/DOC-6063/commands/acl-dryrun/
https://redis.io/docs/staging/DOC-6063/commands/acl-genpass/
https://redis.io/docs/staging/DOC-6063/commands/acl-getuser/
https://redis.io/docs/staging/DOC-6063/commands/acl-help/
https://redis.io/docs/staging/DOC-6063/commands/acl-list/
https://redis.io/docs/staging/DOC-6063/commands/acl-load/
https://redis.io/docs/staging/DOC-6063/commands/acl-log/
https://redis.io/docs/staging/DOC-6063/commands/acl-save/
https://redis.io/docs/staging/DOC-6063/commands/acl-setuser/
https://redis.io/docs/staging/DOC-6063/commands/acl-users/
https://redis.io/docs/staging/DOC-6063/commands/acl-whoami/
https://redis.io/docs/staging/DOC-6063/commands/acl/
https://redis.io/docs/staging/DOC-6063/commands/append/
https://redis.io/docs/staging/DOC-6063/commands/asking/
https://redis.io/docs/staging/DOC-6063/commands/auth/
https://redis.io/docs/staging/DOC-6063/commands/bf.add/
https://redis.io/docs/staging/DOC-6063/commands/bf.card/
https://redis.io/docs/staging/DOC-6063/commands/bf.exists/
https://redis.io/docs/staging/DOC-6063/commands/bf.info/
https://redis.io/docs/staging/DOC-6063/commands/bf.insert/
https://redis.io/docs/staging/DOC-6063/commands/bf.loadchunk/
https://redis.io/docs/staging/DOC-6063/commands/bf.madd/
https://redis.io/docs/staging/DOC-6063/commands/bf.mexists/
https://redis.io/docs/staging/DOC-6063/commands/bf.reserve/
https://redis.io/docs/staging/DOC-6063/commands/bf.scandump/
https://redis.io/docs/staging/DOC-6063/commands/bgrewriteaof/