docs(GlChartSeriesLabel): Add stories related to common usage scenarios

What does this MR do?

This MR adds more stories that resemble usage scenarios from the GitLab project for the GlChartSeriesLabel component.

These stories will provide reference for the update of the GlChartSeriesLabel component as required by this issue #927 (closed)

Basically, the build process will generate the needed storyshots that provide valuable warnings in case something breaks the layout.

The visual layout bugs surfaced by the storyshots (e.g. the one in the tooltip) will be fixed by the following MR: !1650 (merged)

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • GitLab: mr_url
  • Customers Portal: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.