WPB-15157 App crashes after receiving links in a group chat

PR Submission Checklist for internal contributors

• The PR Title

  • conforms to the style of semantic commits messages¹ supported in Wire's Github Workflow²
  • contains a reference JIRA issue number like SQPIT-764
  • answers the question: If merged, this PR will: ... ³

• The PR Description

  • is free of optional paragraphs and you have filled the relevant parts to the best of your ability

What's new in this PR?

Issues

When self user receives a message in which he/she is mentioned more than once, the app crashes as long as this message is the last one for the given conversation:
java.lang.IllegalArgumentException: Key "[email protected]" was already used

Causes (Optional)

When making a query, we left-join MessageMention with self_user_id or null if there are no mentions in last message for self user, however, this table has primary key consisting of not only message_id and conversation_id which means that there can be more than one mention in a given last message, moreover - self user can be mentioned more than once and that's what happens - self user has two mentions in last conversation message and then left-join creates two rows for the given conversation with both mentions.

Solutions

Count self user mentions and group results by conversation_id so that we're sure that there will only be a single row for each conversation.
When I was analysing and making tests of different approaches to find optimal one back then (#3098) I also noticed that having group by conversation_id doesn't affect the execution time, so it should be safe to use that.

PR Post Submission Checklist for internal contributors (Optional)

• Wire's Github Workflow has automatically linked the PR to a JIRA issue

PR Post Merge Checklist for internal contributors

• If any soft of configuration variable was introduced by this PR, it has been added to the relevant documents and the CI jobs have been updated.

References

1. https://sparkbox.com/foundry/semantic_commit_messages
2. https://github.com/wireapp/.github#usage
3. E.g. feat(conversation-list): Sort conversations by most emojis in the title #SQPIT-764.