[Tour of Beam] [Task] Update Playground saveSnippet endpoint to allow updates of snippets

[olehborysevych]

What needs to happen?

Update Playground saveSnippet endpoint to allow updating snippets for authenticated ToB users

• update snippet model
• Update unit tests
• Update integration tests

Issue Priority

Priority: 3

Issue Component

Component: beam-playground

[eantyshev]

.take-issue