Enhance Config to support type and value checking. More detailed errors

[LoicPoullain]

Issue

Fixes #496

Solution and steps

• Add ConfigNotFoundError
• Add ConfigTypeError
• Add Config.get2
• Add Config.getOrThrow
• Update Foal's components to use the new methods instead of Config.get.
• Update the template src/index.ts (and others?).
• Update getAjvInstance tests (check behavior and invalid types).

Checklist

• Add/update/check docs (code comments and docs/ folder).
• Add/update/check tests.
• Update/check the cli generators.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (v1-7-0@f6378be). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             v1-7-0     #641   +/-   ##
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  Coverage          ?   99.64%           
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  Files             ?       94           
  Lines             ?     1687           
  Branches          ?      381           
=========================================
  Hits              ?     1681           
  Misses            ?        6           
  Partials          ?        0

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[LoicPoullain]

The acceptance tests in Bash are failing but this is normal since the CLI install version 1.6