Add grandchild examples to OCO and OUO orders

[AlexCatarino]

Bracket and OTO already have grandchild examples. This adds them to One Cancels Other and One Updates Other: the Place Related Orders sections name grandchildren, and each page gets an Example 2.

• OCO: the take profit triggers a buy-back bracket, whose exit orders are grandchildren of the take profit.
• OUO: the stop loss triggers a short-entry bracket that reverses the position.

The examples use the order factory from QuantConnect/Lean#9828, so they aren't marked testable yet.

Test plan

• docs-style linter passes on both pages.
• Checked the chain and cancel rules in the Add contingent orders: OCO, OTO, OUO and brackets Lean#9828 OrderContingency.Relate and ContingentOrderProcessor.