fix: make burn and issuance timeframe consistent and legible

[rajivpo]

Think timeframes for burn/issuance should be consistent as generally that's what's expected in standard reporting. Also added a small disclaimer in the tooltip to ensure that folks know that it's based on last 6 months of data annualized as opposed to d7 for issuance and since burn for burn. I would use trailing 1yr data but don't see it in the /api/v2/fees/gauge-rates response.

If H1 is just considering H1 as opposed to last 6 months might be worthwhile to add support for trailing 1yr via the backend.