Please update to a newer version

I suggest you report a bug. Ubuntu is not a rolling release distribution and packages can be left in favour of developing ones with issues.

If the bug and security fixes are significant or the version in the repositories is no longer supported then the package may be updated sooner rather than later. You may also find a PPA here on Launchpad.net to upgrade with but this obviously comes with the usual caveats of a PPA.

Thanks for your answer. Yes, Ubuntu is not a rolling release distribution. But even Debian has a newer version of prometheus. Is it possible to upgrade the package of the bionic release (2.10.x) up to 2.7.x (equal to disco release)? I think, that should solve our problem. I also think, that using PPAs is the last option for us, especially in a LTS version.

Is it possible to install the version of a newer Ubuntu release via apt (with a custom apt setting or so)?

You can use dpkg in command line but installing a package from a newer version of Ubuntu isn't recommended. You will also need to satisfy deps of the package, the deps of the deps and so forth.

If there is a newer version of the package in a newer version of Ubuntu then just upgrade to that version and you will have fewer issues as well as a supportable OS.

I thought LTS means 'long term support'... In my opinion this not means that there is no new release for a package after a half year.
Unfortunately it is not an option for us to go away from an LTS version for only one package.

There will be new releases if the version in the repositories is no longer supported or a significant issue is found. LTS just means the release is supported for 5 years. Packages will be provided for this time as well as support from Canonical and the Ubuntu community.

Manfred Hampl suggests this article as an answer to your question:
FAQ #3037: “no rolling release”.

Thanks Manfred Hampl, that solved my question.