Explain how the button can help users and what it selects

[nadinevehling]

We want to clarify what baseline and selection is. This was improved because of matching colors of green and red for comparison.

Still, we received lots of feedback that users don't know how the selection is made Miro:

• "I have no idea what the "Investigate errors" button would do."
• "How did I make the selection?”
• "I'm still trying to get a grasp on what this is trying to show me.
• I'm not 100% sure what my selection is. Maybe it's what I have filtered up here, but I don't know because I don't remember making a selection beyond the time range and those filters. But what did I do to get here again? I clicked on investigate errors and, let's just jump over here. What does that cost to change? Nothing really?"
• "Are these spans from different places?" Immediately selected “Investigate errors” but wondered about the selection. "Why are they considered errors, do they reach a certain threshold?” Panels: “What does each bar present?”"

Short-term solution:

1. Explain in a tooltip how the button can help users and what it selects. Content TBD please check with @knylander-grafana
   

2. Additionally, if the tooltip isn't sufficient, let's add a description in the large errors panel about the selection once the "Investigate errors" button has been selected.
   Design link

[knylander-grafana]

Related: https://github.com/grafana/tempo-squad/issues/458