Add the _install-dependencies task and call it from make config (nhs-england-tools#144)

<!-- markdownlint-disable-next-line first-line-heading -->
## 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](nhs-england-tools#131).

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

## Type of changes

<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply. -->

- [ ] Refactoring (non-breaking change)
- [x] 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

<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->

- [ ] I am familiar with the [contributing
guidelines](../docs/CONTRIBUTING.md)
- [ ] 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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privacy, we kindly ask you to NOT including [PII (Personal Identifiable
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Author: regularfry

Makefile

@@ -24,8 +24,7 @@ clean:: # Clean-up project resources (main) @Operations
 
 config:: # Configure development environment (main) @Configuration
 	# TODO: Use only 'make' targets that are specific to this project, e.g. you may not need to install Node.js
-	make \
-		terraform-install
+	make _install-dependencies
 
 # ==============================================================================
 

scripts/init.mk

@@ -41,9 +41,15 @@ githooks-run: # Run git hooks configured in this repository @Operations
 		--all-files
 
 _install-dependency: # Install asdf dependency - mandatory: name=[listed in the '.tool-versions' file]; optional: version=[if not listed]
+	echo ${name}
 	asdf plugin add ${name} ||:
 	asdf install ${name} $(or ${version},)
 
+_install-dependencies: # Install all the dependencies listed in .tool-versions
+	for plugin in $$(grep ^[a-z] .tool-versions | sed 's/[[:space:]].*//'); do
+		make _install-dependency name="$${plugin}"
+	done
+
 clean:: # Remove all generated and temporary files (common) @Operations
 	rm -rf \
 		.scannerwork \
@@ -138,6 +144,7 @@ HELP_SCRIPT = \
 # ==============================================================================
 
 ${VERBOSE}.SILENT: \
+	_install-dependencies \
 	_install-dependency \
 	clean \
 	config \