Add support for ajv-i18n to localize validation messages

[m-karnam]

Current behavior:

• Validation errors produced by yaml-language-server are always in English.
• For example: Value is above the maximum of 9500.

Problem:

• Applications embedding monaco-yaml want to show validation errors in the user's preferred language.
• AJV (which yaml-language-server uses) already supports ajv-i18n, but there’s no way to configure or enable it in yaml-language-server.

Proposed solution:

• Add a configuration option to specify which ajv-i18n localization should be applied to AJV error messages.
• Example configuration:

  {
    "yaml.validation.language": "fr"
  }

[datho7561]

There's an existing method to pass the locale to the language server, it should be passed in during the initialize request (see https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initialize).

As of 1.19.1, the extension should translate most error messages if the locale is passed in the initialize request.

AJV is currently used to validate referenced schemas (i.e. validate the JSON schema, not validate the YAML document opened), so most errors shouldn't be from AJV (they will only appear if the schema is invalid). However, we should still translate those.