Doc: Provide example of launchplan chaining

[fg91]

We provide an example how to chain tasks and sub workflows with the >> operator. I was recently asked by a user whether this works for launchplans as well as we don't provide an example for this case.
As this does in fact work, I'm adding an example in this PR.

[thomasjpfan]

We'll also need to update this:

https://github.com/flyteorg/flyte/blob/eeac1014362204aba86985253964595990465f12/docs/user_guide/advanced_composition/chaining_flyte_entities.md?plain=1#L32

So the changes appear in the docs.

[thomasjpfan]

Syncing with master so you get #1784 should fix the CI.

[fg91]

We'll also need to update this:

https://github.com/flyteorg/flyte/blob/eeac1014362204aba86985253964595990465f12/docs/user_guide/advanced_composition/chaining_flyte_entities.md?plain=1#L32

So the changes appear in the docs.

flyteorg/flyte#6317 Already done but I'll need to adapt the commit sha after merging this pr @thomasjpfan