Clarified role syntax and scoping in crash course

[james-whiteside]

What is the goal of this PR?

To clarify the syntactic use of role labels in queries, and the scope in which labels apply. This is particularly with regard to the use of unscoped role labels that are the same as the labels of data-storing types.

What are the changes implemented in this PR?

• Improved introduction of roles in the "new users" pathway.
• Changed role name in "new users" pathway to introduce label scoping later on.
• Added clarification in each crash course as to scoping syntax in plays statements.
• Added a clarifying note to each crash course explaining label scoping.

[typedb-bot]

PR Review Checklist

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Trivial Change

• This change is trivial and does not require a code or architecture review.

Code

• Packages, classes, and methods have a single domain of responsibility.
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• The code is canonical and the minimum required to achieve the goal.
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• Logic and naming has clear narrative that communicates the accurate intent and responsibility of each module (e.g. method, class, etc.).
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Architecture

• Any required refactoring is completed, and the architecture does not introduce technical debt incidentally.
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