Add weights to Type of Work Charts

Problem to solve

Some of ours users don't monitor number of tasks, but weights. As a result they cannot use the graphs we created here: https://gitlab.com/gitlab-org/gitlab-ee/issues/12260 in order to monitor how much of the different types of work they are going through,

Intended users

EMs, PMs, Directors of Engineering

Further details

Proposal

Add ability to switch between tasks and weights on the type of work and type by stage diagrams. We will not cover weights in the type by stage diagram for this iteration due to the complexity of having multiple jobs and MRs for the same issue (we currently don't have weights on anything but issues)

Permissions and Security

Inline with the rest of the analytics pages now, this feature will be available for Premium users only.

Users should only see groups/projects/subgroups that they have a reporter access to and above.

For gitlab.com, we will only show the groups, projects, subgroups that fall under namespaces of silver (aka premium) and above.

Documentation

Testing

What does success look like, and how can we measure that?

A user is able to see the weight of issues with different labels in a specific timeframe

What is the type of buyer?

Links / references

Solution

Show issues	Show MRs

We add an additional segmented control when 'Issues' is selected in the 'Show' segmented control. This one has two options: 'Issues' and 'Issue weights'.

When 'Merge requests' is selected in the first segmented control we hide the second one as it's not applicable.

This solution applies to both dropdowns ('Tasks by type' and 'Tasks by stage').