sonar-audit should check for branches that have been analyzed only once

[okorach]

In the life of a project, each long living branch code is supposed to evolve over time. If the branch has been analyzed only once in a given period - 6 months by default - and the branch is marked as keep when inactive) i's likely to be an accidental analysis of a branch that should not be kept. sonar-audit should issue a warning

cc @sylvain-combe-sonarsource