Typos - Insights section

[benNew89]

SPG review: Insights section

This PR addresses spelling, punctuation, and grammar issues found across the three pages in the Insights section of the CircleCI docs.

Using Insights (insights.adoc)

• Added hyphen to "24-hour" as a compound modifier before "delay"

Test Insights (insights-tests.adoc)

• Fixed "Average test per run" → "Average tests per run"
• Fixed "Flakey" → "Flaky" in image alt text

Insights metrics glossary (insights-glossary.adoc)

• Fixed "workflows executions" → "workflow executions" in the Workflow Runs definition
• Fixed "workflows runs" → "workflow runs" in the Total Workflow Duration definition
• Fixed missing space in Overall Success Rate formula: Runs/ → Runs /
• Standardised capitalisation of "Calculated by" across Success Rate and Overall Success Rate definitions
• Fixed missing period at end of the trend colour description paragraph
• Fixed missing space in Throughput formula: builds/ → builds /
• Removed stray closing parenthesis in the MTTR definition