docs: DOC-574: Titles and Legends doc

[jnumainville]

Adds docs for basic info on titles and legends

[dsmmcken]

Needs to be added to sidebar as well.

Can you also include examples for how to hide the legend and how to position the legend on the top/bottom/left/right, which seem to be common AI questions? (Likely update_figure?)

[jnumainville]

I do have one example in the unsafe_update_figure doc for location. Would that example be better housed here or should I link to that document and add the remaining examples there? I'd lean to linking to that doc for the moment as I know we would like to add legend options directly eventually.

[dsmmcken]

I feel like as a user I would have looked in this doc for anything related to legends based on the title being "titles and legends". I get the argument for putting it in unsafe update though.

I would be tempted to put all legends stuff in here, and then link to unsafe_update in any explanatory text.

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[dsmmcken]

looks good, minor typo.

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