Orders API Client Support For Multiple Fallback Bundle(s)

[asonnenschein]

GH Ticket: #1105

This MR adds support in the Orders SDK and CLI for specifying multiple fallback bundles, updates the docs, and updates the orders CLI and SDK tests with success and failure cases for fallback bundles.

CLI example:

planet orders request --item-type "PSScene" \
    --bundle "analytic_8b_udm2" \
    --fallback-bundle "analytic_udm2,analytic_3b_udm2" \
    --name "my order" \
    "20250130_035211_69_2516"

SDK example:

order_request.product(
    ["20250130_035211_69_2516"],
    "analytic_8b_udm2",
    "PSScene",
    "analytic_udm2,analytic_3b_udm2"
)

[ceholden]

I think this looks great and will fulfill the feature request, thank you! I had a couple suggestions about docstrings and a suggestion to cover the fallback_bundle: list[str] case in the tests added in this PR, but nothing functional to change. Nice work and thanks for incorporating into the user guide!