Exit installer if dpkg lock is held for more then 30 seconds

[yubiuser]

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What does this PR aim to accomplish?:
Fixes #3977.

When installing via apt we use a function to check if dpkg is holding a lock on /va/lib/dpkg/lock. If so we wait...until the lock is lifted. If there is no lifting we wait until forever.
This PR adds a safety check to stop the whole installer if the lock is not lifted within 30 seconds.The original PR #1286 already introduced a counter but never used it. We do use it now.

P.S. The PR additionally moves the function test_dpkg_lock out of package_manager_detect because it is not used in there. (Only later in install_dependent_packages)

[PromoFaux]

No issue with this in theory, nobody wants an infinite loop with no user feedback, is 30 seconds a sensible default?

[yubiuser]

We can easily make it 60 seconds or more.... but at some point users will cancle the installer hard because they think it got stuck.

[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-ftl-v5-15-web-v5-12-and-core-v5-10-released/54987/1