Model Experiments: Add menu item to MLflow usage example

...periment_tracking/components/model_experiments_header.vue

...nt_tracking/routes/candidates/show/ml_candidates_show.vue

...tes/experiments/index/components/ml_experiments_index.vue

..._tracking/routes/experiments/show/ml_experiments_show.vue

...s/javascripts/pages/projects/ml/experiments/show/index.js

app/views/projects/ml/experiments/show.html.haml

locale/gitlab.pot

...ment_tracking/components/model_experiments_header_spec.js

...experiments/index/components/ml_experiments_index_spec.js

...cking/routes/experiments/show/ml_experiments_show_spec.js