Add jq as dependency and remove json_extract

[yubiuser]

What does this PR aim to accomplish?:

Adds jq as dependency and removes the now obsolete json_extract function.
jq is a small dependency and adds powerfull json abilities. With FTL v6 we will have a whole new json-based API where jq might be needed anyway. Also for PADD to interact with FTL v6, jq will be a requirement: pi-hole/PADD#247

---

By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code and I have tested my changes.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

---

• I have read the above and my PR is ready for review. Check this box to confirm

[yubiuser]

Example

curl -s 'https://api.github.com/repos/pi-hole/pi-hole/releases/latest' 2> /dev/null | jq --raw-output .tag_name
v5.11.4

[yubiuser]

Needs re-approval, needed to FP to sign all commits.

[RSickenberg]

Did you tested this on a raspbian bullseye ?

I cannot install it bc apparently the version is not available. https://discourse.pi-hole.net/t/opt-pihole-updatecheck-sh-line-47-jq-command-not-found/57789

[yubiuser]

Yes, all installer dependencies are automatically tested in our test suite:
https://github.com/pi-hole/pi-hole/runs/8011149481?check_suite_focus=true

[RSickenberg]

@yubiuser Ok, it appears it was linked to raspbian bulleyes repo, If I changed the sources to buster it all went ok.