[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.)

A solicitação diz respeito ao posicionamento de anotações e imagens de layout, usando o comportamento existente de title_xref e title_yref como referência. Comece rastreando como as opções xref e yref são tratadas para anotações e imagens e, em seguida, compare isso com o posicionamento do título em relação ao container. Considera-se concluído quando container for compatível tanto com anotações quanto com imagens sem causar regressões no posicionamento em relação ao eixo ou na área de plotagem; a questão do tamanho da imagem em pixels fixos pode exigir um escopo separado.