[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 solicitud se refiere al posicionamiento de anotaciones e imágenes del layout, usando como referencia el comportamiento existente de title_xref y title_yref. Empieza trazando cómo se gestionan las opciones xref y yref para las anotaciones y las imágenes, y después compáralo con el posicionamiento del título respecto al container. Se considera terminado cuando container sea compatible tanto con las anotaciones como con las imágenes sin provocar regresiones en la colocación respecto al eje o en el área de trazado; la cuestión del tamaño de imagen en píxeles fijos puede requerir un alcance separado.