[Feature request] Allow annotations and layout images to be positioned relative to the container, not just the x/y axes or plotting area

One thing I really appreciate about title positioning in Plotly is that I can set title locations relative to the container, not just the plotting area or x axis, via the title_xref and title_yref settings. This makes it much easier to achieve consistent title placement across different charts, as many different factors can change the shape of the plotting area.

Would it be possible to add container as an xref and yref option for annotations and images also? I've been needing to manually adjust these across charts, which can take a decent amount of time. (For PNG exports, I can achieve consistent placements by adding them in via Pillow, but this won't help for HTML-based charts.)

Also, one somewhat-related question (which I'm happy to move to a separate issue if needed): Is there a way to ensure that an image will always be the same size, in pixels, as long as the width of the chart (in pixels) is always the same? It appears that, even when the sizex and sizey settings stay the same, the image size can vary. (Since these values are relative to the chart's area, though, this is probably to be expected. But being able to specify a fixed size, e.g. 300x200px, would be fantastic.)

La demande concerne le positionnement des annotations et des images de layout, en prenant comme référence le comportement existant de title_xref et title_yref. Commencez par retracer la manière dont les options xref et yref sont gérées pour les annotations et les images, puis comparez-la au positionnement du titre par rapport au container. C'est terminé lorsque container est pris en charge à la fois pour les annotations et les images sans régression du placement par rapport à l'axe ou dans la zone de tracé ; la question de la taille d'image en pixels fixes devra peut-être faire l'objet d'un périmètre distinct.