Update MR Templates (add "legacy" one)

See changes, modifies the templates to include changes to the package one and the old format for general MRs.

.gitlab/merge_request_templates/general_mr.md

+Summary
+
+(Summarize the purpose of the MR)
+
+Relevant logs/screenshots
+
+(Include any relevant logs/screenshots)
+
+/label ~label
+/assign @someone
+/cc @someoneelse