feat: Adds tree pollen heatmap example.

[willum070]

This change adds the tree pollen heatmap example map.

Fixes #<issue_number_goes_here> 🦕

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 2 region tags.

• samples/tree-pollen/index.ts:7, tag maps_tree_pollen
• samples/tree-pollen/style.scss:9, tag maps_tree_pollen

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