feat: show features without border & ability to add a custom marker

[jessicamcinchak]

two styling features to help clarify how we highlight addresses:

• boolean property featureBorderNone to control whether or not to show a border when highlighting an OS Feature that intersects with a point
  <my-map zoom="20" showFeaturesAtPoint featureFill="#fff" featureBorderNone />
  

• boolean property showMarker to show a marker on the map (defaults to center latitude & longitude), with optional number properties markerLatitude, markerLongitude to specify a custom latitude & longitude to place the marker at. The marker will default to a black dot, but you can pass a custom hex code or CSS color name to markerColor.
  <my-map zoom="20" showMarker />
  

[netlify]

✅ Deploy Preview for oslmap ready!

Name	Link
🔨 Latest commit	fa32965
🔍 Latest deploy log	https://app.netlify.com/sites/oslmap/deploys/62c42821e60e490009f5e5b3
😎 Deploy Preview	https://deploy-preview-159--oslmap.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[jessicamcinchak]

Auto-property colour (instead of outline)?

[gunar]

Nit: I tend to favor positive naming schemes (e.g. featureBorder = true) as to avoid double negation (e.g. featureBorderNone = false).

[jessicamcinchak]

See #37 - had originally defaulted to positive naming schemes for boolean properties, but then learned overtime that it doesn't play so nice with Lit so now consistently declaring all boolean props false by default.