Add-JiraIssueComment - Remove role name restrictions

[bmdixon]

Context

I know there is #174 which is a larger improvement to adding comments but I'm currently only blocked due to the validation on https://github.com/AtlassianPS/JiraPS/blob/master/JiraPS/Public/Add-JiraIssueComment.ps1#L36. I don't have those roles defined so can't use them and need to specify a different/custom role when adding a comment. Could this validation be removed so other roles can be specified? The current list appears to be rather arbitrary and I can't see any reason that these roles are hard-coded.

[bmdixon]

This also affects https://github.com/AtlassianPS/JiraPS/blob/master/JiraPS/Public/Add-JiraIssueWorklog.ps1#L44