Add optional download requirements for dev and plotly express

[ndrezn]

Closes #2279

This PR adds the ability to install Plotly with:

pip install plotly[pandas]

which bundles pandas in the install, required by plotly.express and:

pip install plotly[dev]

which installs dev requirements for the package.

This also revises the warning when using plotly.express if pandas is not installed.

Open to ideas on better wording.

(plotly.py) ➜  plotly.py git:(better-pandas-warning) python
Python 3.12.3 (main, Apr  9 2024, 08:09:14) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import plotly.express
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/nathandrezner/Plotly/plotly.py/packages/python/plotly/plotly/express/__init__.py", line 10, in <module>
    raise ImportError(
ImportError: Plotly Express requires pandas to be installed. You can install pandas using pip with:

$ pip install pandas

Or install Plotly Express and its dependencies directly with:

$ pip install "plotly[pandas]"

You can also use Plotly Graph Objects to create a large number of charts without installing
pandas. See examples here: https://plotly.com/python/graph-objects/

[ndrezn]

We can plausibly drop the note about graph objects but basically I want some sort of explanation of why pandas isn't a dependency.

[emilykl]

We shouldn't recommend pip install plotly.express , I believe it only exists for backwards compatibility and it's confusing to have multiple install paths.

If we want to have a one-liner "install everything" command that should be a change made inside Plotly.py.

[ndrezn]

I was thinking of adding:

pip install plotly[express]

as an option which goes with usual pip patterns for optional dependencies. If we went that route I would expect that we drop support for pip install plotly.express entirely.

[ndrezn]

@gvwilson there are other changes following @emilykl 's comment. It might make sense to break this into two PRs to be honest...

[gvwilson]

:+1: on breaking the PR - thank you

[emilykl]

IMO the naming should be plotly[pandas] rather than plotly[express] -- much more clear what it's actually doing.

I'm in favor of this change, but let's not merge it right away. This PR changes a number of lines in setup.py so it's not just an addition; it could feasibly break the install process for some users. Need to do really solid QA to make sure it runs smoothly.

[ndrezn]

@gvwilson on further thought I think it makes sense to keep these changes in one PR. The text in the warning message is directly related to the installation recommendations that are also added in this PR -- I've updated the title & description to make the primary change more clear.

[gvwilson]

:+1: