Add number type to `annotations.text` chart schema

[chriddyp]

Similar to #2519 , in plotly/plotly.py#942 we're updating plotly.py's validation logic to automatically use the plotly.js schema.

Annotations allow numbers as text (https://codepen.io/chriddyp/pen/WzgxwK) and it's a pretty common use case in the Python library to directly pass data into the text field.

Could we add number to the valid types in the annotations schema? It's currently:

 "text": {
 "valType": "string",
 "role": "info",
 "editType": "calc",
 "description": "Sets the text associated with this annotation. Plotly uses a subset of HTML tags to do things like newline (<br>), bold (<b></b>), italics (<i></i>), hyperlinks (<a href='...'></a>). Tags <em>, <sup>, <sub> <span> are also supported."
 },

[alexcjohnson]

Better: you can look at whether the attribute includes strict: true - if it does, the value must be explicitly a string, and numbers will be rejected. If it does not, we accept numbers (and ONLY numbers - not booleans or any other types) and will coerce them to strings during supplyDefaults.

[chriddyp]

ah very nice, that should work. fyi @jmmease