[BUG]: `vertical_spacing` argument for `make_subplots` should leave space for subplot titles

Description

Setting the vertical_spacing argument of make_subplots to a small value, while also passing subplot_titles, results in a really ugly chart where the subplot titles overlap the subplots themselves.

Ideally vertical_spacing should take titles into account, and control the spacing between the top of the title and the bottom of the subplot above.

We obviously don't know the exact size of the title text, but something like font size * 1.75 should be approximately the right amount of space for a single-line title.

However we need to see whether this requires changes to Plotly.js, since axis.domain only supports units of plot fraction, not sure if there is a way to shift it by a certain number of pixels.

Screenshots/Video

Steps to reproduce

from plotly.subplots import make_subplots
import plotly.graph_objects as go
import random

fig1 = make_subplots(
        rows=6, cols=1,
        shared_xaxes=True,
        vertical_spacing=0.02,
        row_heights=[0.35, 0.13, 0.13, 0.13, 0.13, 0.13],
        subplot_titles=['Heart Rate Variability', 'Walking', 'Cycling', 'Hiking', 'Other', 'Pilates']
    )
for i in range(6):
    fig1.add_trace(
        go.Scatter(x=[0,1,2], y=[random.randint(0, 10) for _ in range(3)]),
        row=i+1,
        col=1
    )
fig1.show()