text: Title: leafmap.add_raster only recognizes some colormap names?
  Body: <!-- Please search existing issues to avoid creating duplicates. -->
  
  ### Environment Information
  
  -   leafmap version: 0.42.6
  -   Python version: 3.12.3
  -   Operating System: Ubuntu 24.04.1
  
  ### Description
  
  leafmap seems to recognize only a (very) limited range of matplotlib colormap names.
  
  ### What I Did
  
  ```
  import leafmap
  
  m = leafmap.Map()
  
  m.add_raster('output/freq.tif', vmin=0, vmax=100, colormap = 'rainbow')
  
  m
  ```
  
  This works fine (freq.tif is a single band GTiff float32 file with values between 0 and 100).
  
  ```
  
  m.add_raster('output/freq.tif', vmin=0, vmax=100, colormap = 'Blues')
  
  m
  ```
  
  throws:
  
  ```
  ---------------------------------------------------------------------------
  ValueError                                Traceback (most recent call last)
  Cell In[6], line 5
        1 import leafmap
        3 m = leafmap.Map()
  ----> 5 m.add_raster('output[/freq.tif](http://localhost:8888/freq.tif)', vmin=0, vmax=100, colormap = 'blues')
        7 m
  
  File [/opt/conda/lib/python3.11/site-packages/leafmap/leafmap.py:2384](http://localhost:8888/opt/conda/lib/python3.11/site-packages/leafmap/leafmap.py#line=2383), in Map.add_raster(self, source, indexes, colormap, vmin, vmax, nodata, attribution, layer_name, layer_index, zoom_to_layer, visible, opacity, array_args, client_args, **kwargs)
     2381 if isinstance(source, np.ndarray) or isinstance(source, xr.DataArray):
     2382     source = common.array_to_image(source, **array_args)
  -> 2384 tile_layer, tile_client = common.get_local_tile_layer(
     2385     source,
     2386     indexes=indexes,
     2387     colormap=colormap,
     2388     vmin=vmin,
     2389     vmax=vmax,
     2390     nodata=nodata,
     2391     opacity=opacity,
     2392     attribution=attribution,
     2393     layer_name=layer_name,
     2394     client_args=client_args,
     2395     return_client=True,
     2396     **kwargs,
     2397 )
     2398 tile_layer.visible = visible
     2400 self.add(tile_layer, index=layer_index)
  
  File [/opt/conda/lib/python3.11/site-packages/leafmap/common.py:3002](http://localhost:8888/opt/conda/lib/python3.11/site-packages/leafmap/common.py#line=3001), in get_local_tile_layer(source, port, debug, indexes, colormap, vmin, vmax, nodata, attribution, tile_format, layer_name, client_args, return_client, quiet, **kwargs)
     3000 else:
     3001     if tile_format == "ipyleaflet":
  -> 3002         tile_layer = get_leaflet_tile_layer(
     3003             tile_client,
     3004             port=port,
     3005             debug=debug,
     3006             indexes=indexes,
     3007             colormap=colormap,
     3008             vmin=vmin,
     3009             vmax=vmax,
     3010             nodata=nodata,
     3011             attribution=attribution,
     3012             name=layer_name,
     3013             **kwargs,
     3014         )
     3015     else:
     3016         tile_layer = get_folium_tile_layer(
     3017             tile_client,
     3018             port=port,
     (...)
     3028             **kwargs,
     3029         )
  
  File [/opt/conda/lib/python3.11/site-packages/localtileserver/widgets.py:105](http://localhost:8888/opt/conda/lib/python3.11/site-packages/localtileserver/widgets.py#line=104), in get_leaflet_tile_layer(source, port, debug, indexes, colormap, vmin, vmax, nodata, attribution, **kwargs)
       98     bounds = Union((Tuple(),), default_value=None, allow_none=True).tag(sync=True, o=True)
      100 source, created = get_or_create_tile_client(
      101     source,
      102     port=port,
      103     debug=debug,
      104 )
  --> 105 url = source.get_tile_url(
      106     indexes=indexes,
      107     colormap=colormap,
      108     vmin=vmin,
      109     vmax=vmax,
      110     nodata=nodata,
      111     client=True,
      112 )
      113 if attribution is None:
      114     attribution = DEFAULT_ATTRIBUTION
  
  File [/opt/conda/lib/python3.11/site-packages/localtileserver/client.py:461](http://localhost:8888/opt/conda/lib/python3.11/site-packages/localtileserver/client.py#line=460), in TileServerMixin.get_tile_url(self, indexes, colormap, vmin, vmax, nodata, client)
      458         colormap = json.dumps(colormap)
      459     else:
      460         # make sure palette is valid
  --> 461         palette_valid_or_raise(colormap)
      463     params["colormap"] = colormap
      464 if vmin is not None:
  
  File [/opt/conda/lib/python3.11/site-packages/localtileserver/tiler/palettes.py:31](http://localhost:8888/opt/conda/lib/python3.11/site-packages/localtileserver/tiler/palettes.py#line=30), in palette_valid_or_raise(name)
       29 def palette_valid_or_raise(name: str):
       30     if not is_mpl_cmap(name):
  ---> 31         raise ValueError(f"Please use a valid matplotlib colormap name. Invalid: {name}")
  
  ValueError: Please use a valid matplotlib colormap name. Invalid: blues
  ```
  
  'blues' (or 'Blues') **is** a valid matplotlib colormap name. Most other names do not work either.