Adjust color scale on C-Haines to provide more clarity at top end

**As a** *Forecaster* **I want** *more clarity on the high end of C-haines * **So That** *I can distinguish between different C-haines values instead fo seeing everything as high*

**Additional Context**
- we can start by generating the full range of values and figuring out what we want to use
- enter text here

**Acceptance Criteria**

- [ ] when i look at the map I can see a larger range of readings when present (1-20)
- [ ] when i look at the legend it matches what is on the map
- [ ] back end generates indices int he new buckets
- [ ] the KML is generated with the new buckets
- [ ] the web page continues to be able to display the old buckets and the new buckets

Start by locating the C-Haines index generation, map and legend rendering, KML generation, and web-page handling for the existing buckets. Compare the full 1–20 range with the current buckets; done means the map, legend, backend indices, KML, and old/new web display all agree.

Written by the indexing model from the issue text.