Comment will select all activities filter by default

What does this MR do?

QA::Page::Project::Issue::Show.comment will perform select_all_activities_filter by default unless another filter is specified.

Closes https://gitlab.com/gitlab-org/quality/nightly/issues/107

CE Port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29496

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content