Add the _install-dependencies task and call it from make config

[regularfry]

Description

This adds the make _install-dependencies task, which installs everything from the .tool-versions file.

Context

This avoids the need to add a new make task for each dependency, instead treating the .tool-versions file as canonical. Specifically it avoids the need for the user to add a make _install-python task in the tutorial.

For discussion: do we still need make _install-terraform if we have this? I don't think we do.

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.

[stefaniuk]

LGTM 👍