accept int for rows and cols in `fig.add_traces`

At the moment if you want to add several traces to the same subplot you have to pass an iterable to the rows and cols arguments of fig.add_traces.

import plotly.express as px
df = px.data.tips()
fig = px.scatter(df, x='total_bill', y='tip', color='day')
from plotly.subplots import make_subplots
fig2 = make_subplots(1, 2)
fig2.add_traces(fig.data, rows=[1,]*len(fig.data), cols=[1,]*len(fig.data))
fig2.show()

We could also accept an int here, in which case all traces would be added to the same subplot.

[nicolaskruchten]

@MCBoarder289 if you’re interested, solving this issue might involve the same area of the code you were just in 😃

[nicolaskruchten]

Awesome! Please don’t feel any pressure to work on it or anything, I was just flagging it in case you were looking for a (possibly easy) entry-point into another PR here 😃