feat(GlChartTooltip): Add slot API for chart tooltip, remove title prop

What does this MR do?

This change introduces scoped slots to render the chart tooltips that should make it easier its use.

This allows for the tooltip title and content to be changed independently and reduce complexity when customizing them.

Also, removes the "title" prop from the chart tooltips which is not in use by any of the charts.

feat(GlChartTooltip): Add slot API for chart to... (!3824 - merged) • Miguel Rincon • 16.7	you are here
feat(GlLineChart, GlAreaChart): Simplify chart ... (!3825 - merged) • Miguel Rincon • 16.7
[Gitlab UI Integration] feat(GlLineChart, GlAre... (gitlab!138351 - closed) • Miguel Rincon	optional integration step

Why this change?

In the next MR at !3825 (merged), I introduce a change that will allow us to use slots to customize our tooltips. Both changes are backwards compatible, so they simply become an easier way to customize tooltips.

Screenshots or screen recordings

No changes are expected here. We have a comprehensive test suite of our tooltips in cypress $ yarn run cypress open.

Integration merge requests

The MR passes the pipeline, and I have verified it manually:

• GitLab: gitlab!138191 (closed)
• CustomersDot: mr_url
• Status Page: mr_url

Does this MR meet the acceptance criteria?

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• If the MR changes a component's API, integration MR(s) have been opened (see integration merge requests above).
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Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

• All actions and functionality can be done with a keyboard.
• Links, buttons, and controls have a visible focus state.
• All content is presented in text or with a text equivalent. For example, alt text for SVG, or aria-label for icons that have meaning or perform actions.
• Changes in a component’s state are announced by a screen reader. For example, changing aria-expanded="false" to aria-expanded="true" when an accordion is expanded.
• Color combinations have sufficient contrast.