feat: dlt.Schema.to_dot() graphviz export

[zilto]

This follows #2929 and adds DOT export.

Example

Visualize you dlt.Schema inside notebooks (marimo, VSCode, Colab, Databricks, Jupyter, etc.). This requires no additional dependencies. You can also render it to a file (.png, .svg, etc.) using graphviz

Design

• the DOT is produced by handling strings instead of using graphviz. This allows to make it 0 dependency. This is particularly useful because the graphviz Python library depends on graphviz system installs
• add _repr_html_ to dlt.Schema, this method is automatically picked up by notebook renderers. This method wraps the DOT string into an HTML that loads JS bundles from the web to render the viz. This won't work offline
• add render_schema_with_graphviz(). This requires graphviz dependency and allows to render the dlt.Schema as svg, png, jpeg, pdf, etc.
• update CLI commands
• update documentation
• testing is minimal because we can't do DOT -> dlt reliably

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[rudolfix]

LGTM! I'm not sure how many schema converters we'll need in the future but maybe we need to make them pluggable ie. via our existing pluggy and standard interface with schema import/export (it is almost standard btw.)
also some settings could be configurable ie. html template and colors. this is easy to add and we can do it in the future

[rudolfix]

LGTM!