Throw ConfigError when component configs are invalid

[domoscargin]

Closes #4037

What

I've got two approaches here:

Validate within the component class

At the moment, we only need this validation on Character Count, so we could just do a specific validation in that class. Might be good enough for now.

Use a schema

It'd be nice to just use something like AJV and validate a schema, but that'd add weight to our code, so I've implemented a custom validation method on the base component that we can build on as necessary.

It'd also be nice to somehow use our YAML (or compiled JSON fixtures) here, but that's a lot trickier to unpick than is required for this work (for example: how to separate out nunjucks and JS properties, how to document more complex rules like anyOf, etc).

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Update: We've gone with the schema approach and loosely followed:
https://ajv.js.org/packages/ajv-errors.html#single-message

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📋 Stats

File sizes

File	Size
dist/govuk-frontend-4.6.0.min.css	118.07 KiB
dist/govuk-frontend-4.6.0.min.js	47.1 KiB
dist/govuk-frontend-ie8-4.6.0.min.css	79.27 KiB
packages/govuk-frontend/dist/govuk/all.bundle.js	73.57 KiB
packages/govuk-frontend/dist/govuk/all.bundle.mjs	69.08 KiB
packages/govuk-frontend/dist/govuk/all.mjs	3.84 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend-component.mjs	359 B
packages/govuk-frontend/dist/govuk/govuk-frontend.min.js	35.82 KiB
packages/govuk-frontend/dist/govuk/i18n.mjs	5.83 KiB

Modules

File	Size
all.mjs	65.19 KiB
components/accordion/accordion.mjs	20.86 KiB
components/button/button.mjs	3.67 KiB
components/character-count/character-count.mjs	20.6 KiB
components/checkboxes/checkboxes.mjs	4.37 KiB
components/error-summary/error-summary.mjs	4.96 KiB
components/exit-this-page/exit-this-page.mjs	15.42 KiB
components/header/header.mjs	2.3 KiB
components/notification-banner/notification-banner.mjs	3.5 KiB
components/radios/radios.mjs	3.37 KiB
components/skip-link/skip-link.mjs	2.67 KiB
components/tabs/tabs.mjs	8.04 KiB

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