Fix new os_check

[PromoFaux]

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What does this PR aim to accomplish?:

The newly added os_check works fine if dig is already installed... I guess one thing we did not test was a fresh installation!

This PR moves the call to the os_check function to after the installer dependencies are installed, and also moves bind-utils (yum) and dnsutils (apt) to the installer dependencies

If we want to have this at the top of the installer, then we will not be able to use the TXT record on versions.pi-hole.net, and instead will need to curl the same information from somewhere else.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-5-1-released/35577/1