feat(DataPlatform): Introducing optional DataPlatform logoUrl field

[jjoyce0510]

Scope
This PR introduces an optional logoUrl field in the DataPlatformInfo PDL. The motivation is we would like to display platform-specific logos on the UI. This approach will allow us to drive the logo shown in the React experience from the server, as opposed to hardcoding specific logo images in the frontend code on a per-platform basis, with the idea being to reduce the frequency frontend code needs to be updated in cases of customization. It also allows individual organizations to change logos for a particular platform as they wish.

Changes

1. Add optional "logoUrl" field to DataPlatformInfo object (not a breaking change)
2. Update GQL API in datahub-graphql-core to include the optional logoUrl field.

Validation
Validated this change by adding a test logoUrl to DataPlatformInfo.json file locally. Deployed a local version of gms and datahub-frontend, was able to fetch the logoUrl provided in the json configuration file without issue.

Checklist

• The PR conforms to DataHub's [Contributing Guideline](https://github.com/linkedin/datahub/blob/mas ter/docs/CONTRIBUTING.md) (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable)

[shirshanka]

LGTM!