ChannelMemberHistory reference needs to be case sensitive

[sadohert]

Testing the Legal Hold plugin on Mysql (Aurora on AWS).

Was getting this error when the job runs:

{"timestamp":"2024-06-14 13:26:49.084 Z","level":"error","msg":"invalid key/value pair","caller":"app/plugin_api.go:976","plugin_id":"com.mattermost.plugin-legal-hold","arg":"Error 1146 (42S02): Table 'sdohertydb.channelmemberhistory' doesn't exist"}

I think this line is where we are hardcoding to lower case, and where we need to fix this:

mattermost-plugin-legal-hold/server/store/sqlstore/legal_hold.go

Line 116 in 06410e3

From("channelmemberhistory as cmh").

[grundleborg]

Reopening until verified by QA