(build) Use rc prerelease label

When there is no prerelease label, it means we are building on the
master branch, however, when we are not tagged, we still need this
label, otherwise, building the packages fails.  Let's use the rc
(Release Candidate) label.  i.e. building on develop gives us alpha
packages, building on hotfix/release branches gives us beta packages,
and building on master branch without a tag, gives us rc packages.

BuildScripts/default.ps1

@@ -69,8 +69,8 @@ task Run-GitVersion {
         $script:packageVersion = $versionInfo.LegacySemVer
         $script:informationalVersion = $versionInfo.InformationalVersion
     } else {
-        $script:packageVersion = "$majorMinorPatch" + $(if ($prerelease) { "-$prerelease" }) + "-$buildDate" + $(if ($counter) { "-$counter" })
-        $script:informationalVersion = "$majorMinorPatch" + $(if ($prerelease) { "-$prerelease" }) + "-$buildDate-$sha"
+        $script:packageVersion = "$majorMinorPatch" + $(if ($prerelease) { "-$prerelease" } else { "-rc" }) + "-$buildDate" + $(if ($counter) { "-$counter" })
+        $script:informationalVersion = "$majorMinorPatch" + $(if ($prerelease) { "-$prerelease" } else { "-rc" }) + "-$buildDate-$sha"
     }
 
     Write-Host "Assembly Semantic Version: $version"