allow aligning hovertext for annotations

It looks like there is no way to control the text justification for annotation hovertexts. For example:

# Make an background image
f = px.imshow( [[255]*6]*3, origin='lower')

# Add two annotations with hovertext
f.add_annotation( x=1, y=1, text='left', hovertext='Will be left justified<br>*', showarrow=False)
f.add_annotation( x=5, y=1, text='right', hovertext='Will be right justified<br>*', showarrow=False)

# Tighten the plot
f.update_layout( margin={'l':0, 'r':0, 't':0, 'b':0}, coloraxis_showscale=False)

# This will not apply on the annotation hovertext
f.update_layout( hoverlabel_align='left') 

# This does not exist and annotation hovertexts default to auto
# f.update_annotations( hoverlabel_align='left')

f.show()

The image hovertexts will be all properly left-justified, but the annotation hovertexts will default to 'auto', with the left one being left-justified, and the right one being right-justified. Am I missing something, or this is an omission in the tunable options? Is there some other way to force left-justification on the annotation hovertexts? I produce a set of tables that way that look atrocious otherwise.

Thanks!

从 f.add_annotation 中展示的 annotation API 和 f.update_layout 中 hoverlabel_align 的行为入手，然后追踪 annotation hovertext 选项是如何暴露的。完成的标准是 annotation hovertext 可以接收显式的对齐设置，包括 issue 中描述的左对齐和右对齐示例。