Add new IgnoreUnknownAssetHoldings algorithm setting

[jhonabreul]

Description

Add new IgnoreUnknownAssetTypes algorithm setting to indicate brokerages whether we want to receive a warning or error message when subscribing to an asset that they don't support, so that users can decide whether or not the algorithm should be terminated on the situations.

Also wire brokerage message handler before algorithm initialization so that brokerage messages received on initialization or account synchronization (fetching existing holdings, orders and cash balance) can be properly handled and communicated.

Related to QuantConnect/Lean.Brokerages.InteractiveBrokers#134

Related Issue

Motivation and Context

Requires Documentation Change

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which improves implementation)
• Performance (non-breaking change which improves performance. Please add associated performance test and results)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Non-functional change (xml comments/documentation/etc)

Checklist:

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>

[Martin-Molinero]

Thank you!