[RFC]: Bring Flask-GoogleMaps up to date with latest dependencies

[argysamo]

Is your feature request related to a problem? Please describe.

• Flask-GoogleMaps is not compatible with latest Flask 3.0.0 version. As described in [bug] import "Markup" fails when using Flask 3.0+ in __init__.py #157 Markup is not bundled with Flask anymore, and needs to be imported from elsewhere
• Latest Google maps API deprecated Marker and promotes AdvancedMarker instead. AdvancedMarker is much more powerful, as you can use ones with different colours in a very straightforward manner.

Describe the solution you'd like

• Update Flask-GoogleMaps so as to be compatible with latest Flask.
• Remove obsolete (Google Maps) Markers and use AdvancedMarkers instead.

Describe alternatives you've considered

NA

Additional context
NA

[argysamo]

I have started working on the proposed changes and will submit a PR soon.