update transaction diagram

[alexandratran]

Pull request checklist

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Before creating the pull request

Make sure that:

• you have read the contribution guidelines.
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• you have fixed all the issues raised by the tests, if any.
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  and updated the testing link (see Testing).

Describe the change

Update transaction diagram to replace web3js-eea with web3js-quorum and update style for consistency.

Issue fixed

fixes #115

Impacted parts

For content changes

• [ x] Doc content
• Doc pages organisation

For tools changes

• CircleCI workflow
• Build and QA tools (lint, vale,…)
• MkDocs templates
• MkDocs configuration
• Python dependencies
• Node dependencies and JavaScript
• ReadTheDocs configuration
• GitHub integration

Testing

See https://pegasys-ethsigner--123.com.readthedocs.build/en/123/Concepts/Overview/

Screenshots / recording

[bgravenorst]

LGTM