Add tracking for new merge request page

...ntrollers/projects/merge_requests/creations_controller.rb

app/helpers/projects/issues_helper.rb

app/views/projects/issues/_new_branch.html.haml

app/views/projects/merge_requests/_nav_btns.html.haml

app/views/shared/empty_states/_merge_requests.html.haml

config/events/click_create_confidential_mr_issues_list.yml

config/events/click_create_mr_issues_list.yml

config/events/click_new_merge_request_empty_list.yml

config/events/click_new_merge_request_list.yml

config/events/create_mr_web_ide.yml

config/events/visit_after_push_link_or_create_mr_banner.yml

.../count_total_click_create_confidential_mr_issues_list.yml

...cs/counts_all/count_total_click_create_mr_issues_list.yml

...ts_all/count_total_click_new_merge_request_empty_list.yml

...s/counts_all/count_total_click_new_merge_request_list.yml

config/metrics/counts_all/count_total_create_mr_web_ide.yml

...count_total_visit_after_push_link_or_create_mr_banner.yml

...lers/projects/merge_requests/creations_controller_spec.rb

spec/helpers/projects/issues_helper_spec.rb