Add fetch_options for VectorTileLayer

[clydebw]

Related to this issue, this PR adds fetch_options to VectorTileLayer, allowing credentials to be added to vector tile requests.

For example:

lyr = ipyleaflet.VectorTileLayer(
    url=url,
    fetch_options={
        "credentials": "include"
    }
)

...which would allow cookies to be included in vector tile requests.

I've tested these changes manually, and they seem to work.

[clydebw]

Just realising that this failed a bunch of CI Actions. @martinRenou I don't think I changed anything visually here - is this broken? Is there anything I can do to help fix?