Add release note step

[AlexanderVorobyov]

• Add ReleaseNoteData class to build release note text.
• Add ReleaseNoteStep class as build step to create instance of the ReleaseNoteStep data.
• Add ReleaseNoteExportStep class as build step to export ReleaseNoteData data as file.
• Add UnityCloudBuildManifestReleaseNoteStep class as build step to add UnityCloudBuildManifest data to the release notes.

[AlexanderVorobyov]

Create branch from main

issue-28-add-release-note-step