Check versions file on the debug log

[rdwebdesign]

What does this PR aim to accomplish?

Add info about versions file to the debug log.

Context:
Recently we introduced versions file to /etc/pihole directory.
We use this file in a lot of places, but a check for this file was never included in the debug log.

Including this check will show extra info: file last update time, file permissions and file content:

-rw-r--r-- 1 root pihole 291 Oct 13 20:24 /etc/pihole/versions
   CORE_BRANCH=development
   WEB_BRANCH=topboxlink
   FTL_BRANCH=development
   CORE_VERSION=v5.12.2-43-g997a771
   WEB_VERSION=v5.15.1-32-g16823707
   FTL_VERSION=vDev-2de12e2
   DOCKER_VERSION=nightly
   GITHUB_CORE_VERSION=v5.13
   GITHUB_WEB_VERSION=v5.16
   GITHUB_FTL_VERSION=v5.18.2
   GITHUB_DOCKER_VERSION=2022.10

How does this PR accomplish the above?

Adding versions file to the REQUIRED_FILES list.

What documentation changes (if any) are needed to support this PR?

none

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