[config] Add severity mappings for Cppcheck

[coolhill]

This is needed in order to sort and visualize Cppcheck results by severity when converted(report-converter) and stored into a codechecker database.

[coolhill]

Any duplicates is there bc somewhat different checker naming conventions between the tools (capitalization). Severities levels collected from official SEI cert page. L1, L2, L3 = HIGH, MEDIUM, LOW

[whisperity]

Hm. If we are to support severities for external analysers, then this flat structure of the severity map file will bite us in the backside. It should be changed to have a two-level structure, i.e. first grouped by analyser identifier, and then by checker name.

In addition, these changes as of now conflict with #3367, because these new records are not part of the ClangSA/Tidy suite, and as such, aren't reported by CodeChecker checkers, which will make the job report them as "obsolete but existing records".

[csordasmarton]

@whisperity @bruntib already working on it to restructure these configuration files. The patch #3233 is still under discussion but I hope that until the next release it will be merged.

[coolhill]

it makes sense to map severities from the actual severity column and not the level. although I did read something different internally on applying sei cert. anyways it is a simple fix so now HIGH, MEDIUM, LOW = HIGH, MEDIUM, LOW

on a side-note it might be worth noticing that env33-c/ENV33-C and msc30-c/MSC30-C still differ between the tools