PLATFORM-3404 - Allow Alert display type to be overwritten

[woodyblah]

Proposed changes

The Alert container has the class d-flex hardcoded, this PR allows it to be overwritten while keeping the d-flex as the default to allow backwards compatibility.

Types of changes

What types of changes does your code introduce to the project?

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Please use the following checklist before contributing to this repository.

• I have added tests that prove my fix is effective or that my feature works
• I have implemented error checking and considered data not being available or loading
• I have added necessary documentation (if appropriate)
• I have implemented correct type checking
• I have tested my changes on a mobile layout
• I have double checked with the team that I haven't introduced duplicates in functionalities (components, services, database changes, etc...)
• If required, designers have signed off my changes
• I have communicated the changes to the QA team and planned testing
• I have implemented e2e tests for the new functionality