Modify Add-JiraGroupMember so that it honors ErrorAction

[spascoe]

Description

In Add-JiraGroupMember.Unit.Tests.ps1, these two tests require the Add-JiraGroupMember to handle the supplied ErrorAction parameter:

• "Tests to see if a provided user is currently a member of the provided JIRA group before attempting to add them"
• "Gracefully handles cases where a provided user is already in the provided group"

I switched the Write-Error to WriteError and adjusted the splat parameter to supply the necessary parameters

Motivation and Context

This change is necessary to enable the tests to pass.
closes #425

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• I have added Pester Tests that describe what my changes should do.
• I have updated the documentation accordingly.