feat: option to add custom meta tags to the UI container

[pritamsoni-hsr]

What does this PR do?

feature to allow users to add custom meta tags directly to the lightning app.

under the hood, it writes these tags to index.html as the last step in the LightningApp constructor.

Limitation

if a user runs multiple apps on a single machine at the same time the latest tags will be visible in all the apps.

image should be a valid url, rn users cannot provide a local filesystem path.

need to update docs

Does your PR introduce any breaking changes? If yes, please list them.

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Make sure you had fun coding 🙃

[ethanwharris]

LGTM 😃

[kaushikb11]

LGTM!

[awaelchli]

I share same concerns with Thomas about the dependency. Have we looked at the code, are we happy with how it is maintained, how heavy/light it is etc?

[pritamsoni-hsr]

bs4 is around 2MB in size, @awaelchli. I think we should just use it instead of writing parsers from scratch.

[tchaton]

Approving to unblock releasing!