Persist Playground state using workspaceName prop

[BrunoScheufler]

This issue pertains to the following package(s):

• GraphQL Playground - Electron App
• GraphQL Playground HTML
• GraphQL Playground
• GraphQL Playground Express Middleware
• GraphQL Playground Hapi Middleware
• GraphQL Playground Koa Middleware
• GraphQL Playground Lambda Middleware

What OS and OS version are you experiencing the issue(s) on?

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What version of graphql-playground(-electron/-middleware) are you experiencing the issue(s) on?

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What is the expected behavior?

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What is the actual behavior?

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What steps may we take to reproduce the behavior?

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As discussed in the Slack community, I'd like to have the option to pass a workspaceName prop to the Playground React component (PlaygroundWrapper) to persist my Playground state using a specific key. I'll submit a PR with an option to fix this.