NEBULA-1385: Add initialState config for sandbox

[William010x]

Context

JIRA

What changed

• Added initialState with document, headers and variables for embeddable sandbox

How to test

• Checkout to william/sandbox-initial-state on embeddable-explorer repo
• Checkout to william/explorer-everywhere/sandbox-initial-state on studio-ui repo
• Change constants.ts to EMBEDDABLE_SANDBOX_URL = 'https://embed.apollo.local:3000/sandbox/explorer';
• Add an initial state to the embed configuration, for example:

initialState: {
document: `query Test {
  me {
    id
  }
}`,
variables: {
  test: 'abcxyz',
},
headers: {
  'key': 'value'
},

• npm run build-sandbox:umd on embeddable-explorer
• npm run start:embedded on studio-ui
• Open localDevelopmentExample for embedded Sandbox on Go Live
• Close all tabs to see initial state

Corresponding studio-ui PR

[changeset-bot]

🦋 Changeset detected

Latest commit: c6b246c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@apollo/explorer	Minor

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[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

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Latest deployment of this branch, based on commit c6b246c:

Sandbox	Source
npm-embeddable-explorer	Configuration

[mayakoneval]

awesome! lgtm. This should be a minor (feature add)