Github importer allows users to import attachment which exceed the limit set in JIRA

PreConditions:
Set the attachment size limit to 5kb in JIRA

Steps to reproduce:
1. Launch github importer.
2. Try importing issues which has attachments which are more than 5kb.

Expected Behavior:
Importer must respect the attachment limit set by the JIRA.

Actual Behavior:
Importer imports the attachments without respecting the limit set by the JIRA.