Fix Debian/RPM code quality issues

Detailed Description

Summary:

• Fixes all code quality issues reported for the deb/rpm builds.
• CI will enforce that MR builds pass with no code quality issues.
• deb issues may be suppressed using lal*/debian/[source/]lintian-overrides.
• rpm issues may be suppressed using lal*/rpmlintrc.

Issues fixed include:

• Missing man pages. Many help2man-generated pages were not being installed.
• Errors in help2man man page generation. Fix parts of the build system to run binaries from the build tree ("uninstalled") needed for help2man. Fix some programs to parse --help without errors. This should resolve #786 (closed).
• Link library code on Linux with -Wl,--as-needed, which should prevent overlinking to shared libraries.
• Other than lal, replace calls to exit() with abort() in library code. Calling exit() from library code will kill the entire process, whereas abort() can at least be captured for nicer error handling.
• Do not package and install lal*-user-env.* scripts, shouldn't be needed for system-installed packages.
• Fix some missing dependencies, e.g. deb Python packages requiring python3.
• Various other things, see the commit log.

Other changes:

• Rename the [ci debian] and [ci rhel] CI commit message tags to [ci deb] and [ci rpm], for consistency with the other tags; see the updated table in CONTRIBUTING.md.
• Fold in commits from !2493 (closed), ensures that all of LALSuite can be compiled with -Og.
• Ports all lint: CI jobs from EL8 to Conda images, to access newer version of Python needed for some code quality checkers.

API Changes

Please tick one of the following options:

• These changes do not modify the API.
• These changes do modify the API, and are backwards compatible.
• These changes do modify the API, and are backwards incompatible.

For examples of changes that do not modify the API and/or are considered backwards (in)compatible, please see the contributing guide.

Justification for Backwards Incompatible Changes

n/a

Review Status

n/a