Fix bugs in brokerage settings docs

Remove cash and holdings properties from the settings of brokerages that don't allow that options
Add cash and/or holdings properties in settings of brokerages that allow that options
Related Issue

Closes #1756

Motivation and Context

With this change the docs will be accurate describing the allowed properties when creating a live algorithm using certain brokerage

Types of changes
[x] Bug fix (non-breaking change which fixes an issue)
[ ] Refactor (non-breaking change which improves implementation)
[ ] New feature (non-breaking change which adds functionality)
[x] Non-functional change (xml comments/documentation/etc)

[x] My code follows the code style of this project.
[x] I have read the CONTRIBUTING document.
[x] My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>

QuantConnect / Documentation