allow runs to reference runs of the same name (i.e. earlier versions of themselve) for the path_gdx

[0UmfHxcvx5J7JoaOhFSs5mncnisTJJ6q]

close #1423

• New feature

Checklist:

• My code follows the coding etiquette
• I performed a self-review of my own code
• I explained my changes within the PR, particularly in hard-to-understand areas
• I checked that the in-code documentation is up-to-date
• I adjusted the reporting in remind2 where it was needed
• I adjusted forbiddenColumnNames in readCheckScenarioConfig.R in case the PR leads to deprecated switches
• All automated model tests pass (FAIL 0 in the output of make test)
• The changelog CHANGELOG.md has been updated correctly

[orichters]

• thanks for testing it
• One remark: If you pushed a config file using that to the repo, it will fail make test-full for others later on this test, because it cannot find the path_gdx
• I suggest catching this case here replacing those lines by:

          if (path_to_gdx == "path_gdx" && iscenarios[iscen, path_to_gdx] == iscen) {
            iscenarios[iscen, path_to_gdx] <- NA
          } else {
            icfg$errorsfoundInConfigureCfg <- sum(icfg$errorsfoundInConfigureCfg, 1)
            message(red, "Error", NC, ": Can't find a gdx specified as '", iscenarios[iscen, path_to_gdx], "' in column ",
                    path_to_gdx, ".\nPlease specify full path to gdx or name of output subfolder that contains a ",
                    "fulldata.gdx from a previous normally completed run.")
          }

[orichters]

I would probably like to use that for the next round of NGFS runs. If you agree with my suggestion above, could we merge this PR, @0UmfHxcvx5J7JoaOhFSs5mncnisTJJ6q?