Improve rendering in DORA4 Lead time chart

Summary

Lone entries with deploy to production on the DORA4 chart (single dates with a data point and no neighbours) are not visible by default, even though they include information on hover:

Default:

Hover:

Steps to reproduce

Go to https://gitlab.com/gitlab-org/gitlab/-/pipelines/charts?chart=lead-time if you're a member of the gitlab-org/gitlab project
Check the graphs

It might be the case the data available at the time you check might not trigger this edge case

Proposal

If the current date has deployments, it should be visually registered in the chart as a dot:

This proposal also:

Adds a 12px dot by default on every date on the chart that has data
Increases the size of dots to 24px on hover

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

Expand for output related to GitLab environment info


(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)