Add troubleshooting article for repository malformed index error

[TraceyC77]

"Error parsing repository index information. Index file does not exist or is malformed."

It's possible to get this doing rollbacks as part of other troubleshooting.

The solution is to delete any index present and download it again. (Per Harvey)

We should probably add the solution to the troubleshooting section of the help center because I have heard of this happening before.

Ref
https://help.getsol.us/docs/packaging/advanced-config/local-repository#creating-or-updating-the-local-repository-index

https://help.getsol.us/docs/packaging/advanced-config/local-repository#adding-the-local-repository-index-to-the-eopkg-repository-database