Remove Ubuntu 16.04, 18.04 and 20.04 products

[evgenyz]

Description:

• Clean up the project, remove obsolete products that are EOL.

Rationale:

• Fixes Remove Old Ubuntu Products (16.04, 18.04, 20.04) #13035

Review Hints:

• I've updated the labs docs with Ubuntu 24.04 references, it should make sense
• Unused rules removal is out of scope of this PR, it is already big enough

[github-actions]

This datastream diff is auto generated by the check Compare DS/Generate Diff

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OVAL for rule 'xccdf_org.ssgproject.content_rule_installed_OS_is_FIPS_certified' differs.
--- oval:ssg-installed_OS_is_FIPS_certified:def:1
+++ oval:ssg-installed_OS_is_FIPS_certified:def:1
@@ -7,7 +7,4 @@
 extend_definition oval:ssg-installed_OS_is_sle12:def:1
 extend_definition oval:ssg-installed_OS_is_sle15:def:1
 extend_definition oval:ssg-installed_OS_is_slmicro5:def:1
-extend_definition oval:ssg-installed_OS_is_ubuntu1604:def:1
-extend_definition oval:ssg-installed_OS_is_ubuntu1804:def:1
-extend_definition oval:ssg-installed_OS_is_ubuntu2004:def:1
 extend_definition oval:ssg-installed_OS_is_ubuntu2204:def:1

[dodys]

overall it looks good to me, just need to agree on Matthew's remarks.

[codeclimate]

Code Climate has analyzed commit 5886f8e and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 61.8% (0.0% change).

View more on Code Climate.