Fix streamlit-folium incompatibility (add layer to map with new class)

[Conengmo]

Fix the compatibility issue between Folium 0.15.0 and streamlit-folium, see randyzwitch/streamlit-folium#148.

When adding layers to the map, don't add the relevant code to the figure object. Instead, add a new class instance to the Layer instance. That way it will get rendered even if only the map and not the figure is being rendered. This is also maybe a bit nicer, since it's more in line with how the rest of Folium works.

[BastienGauthier]

Works for me !

[Conengmo]

pre-commit.ci autofix

[Conengmo]

@ocefpaf when you have a moment, could you make a v0.15.1 release please? I already put an update in the changelog: https://github.com/python-visualization/folium/blob/main/CHANGES.txt

[BastienGauthier]

@ocefpaf, if you have time to do the release before the end of next week it could help me quite a lot for my project actually :)
Thanks !

[Conengmo]

I think all relevant code to publish to PyPI is in our Github Actions, so I'll give it a try to bake a release later today.

[ocefpaf]

I can do this today and I'll write a guide so others can do it in my absence.

[Conengmo]

Sounds good @ocefpaf, thank you!

[ocefpaf]

Sounds good @ocefpaf, thank you!

Done! I thought I broke GHA last time but it was in top condition, so all we have to do is:

0. Go on Draft a new release:
   

1. Type the release number with a prefixed v for the tag, like v0.15.2 and vlick on create new tag on publish.

2. Use the same number for the release version below.

3. Click on the `Generate release notes" (I usually edit that a bit, like removing bot PRs and writing smaller titles).

4. Click on publish and wait for the GHA to submit the artifacts to PyPI. Conda-forge bots usually picks the release up automatically after ~1 hour and you don't need to do anything there.

[Conengmo]

Perfect @ocefpaf, very clear! To be sure, I'll announce any new release in advance.

Let's also stop updating CHANGES.txt from next release onwards. At that time I'll add a line on top to point towards our Github releases. And update our readme as well.

[edit] to be sure we can find this guide again I posted it to the wiki: https://github.com/python-visualization/folium/wiki/How-to-make-a-release