Add usage charts to the observability usage quota page

What does this MR do and why?

The main goal of this MR is to add daily usage charts to the observability usage quota page. As part of this, I've made some small refactoring and extracted some shared logic from ObservabilityUsageBreakdown, and restructure it a bit to keep it more lean.

• Create ObservabilityUsageChart component
• Create ObservabilityUsageSectionedBar component, extracting it from ObservabilityUsageBreakdown
• Add ObservabilityUsageChart and ObservabilityUsageSectionedBar components to ObservabilityUsageBreakdown and cleaned up the template

Close https://gitlab.com/gitlab-org/opstrace/opstrace/-/issues/2829

Needs !158256 (merged)

MR acceptance checklist

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Screenshots or screen recordings

How to set up and validate locally

• Make sure you are logged in and running GDK with Ultimate license
• Enable :observability_metrics, :observability_logs, :observability_tracing feature flags
• Apply patch to load local mocks:

git apply < <(curl -s https://gitlab.com/-/snippets/3725611/raw/main/a.patch)