[Deprecations service] Expose level field to config deprecations

[Bamieh]

Summary

We assumed that all config deprecations are of level critical hence we did not expose this field to the deprecation factory. A few configs are indeed not critical for 8.0 hence allowing devs to override the level make enables warning level deprecations to be addressed by the deprecations service.

Usage:

export const config = {
  schema: configSchema,
  deprecations: () => [
     (rawConfig, fromPath, addDeprecation) => {
        addDeprecation({
          level: 'warning', // optional; Defaults to 'critical' for config deprecations.

          title: i18n.translate(...),
          message: i18n.translate(...),
          correctiveActions: { ... },
        });
     }
  ],
};

Closes #110603

[kibanamachine]

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Metrics [docs]

✅ unchanged

History

• 💚 Build #151813 succeeded 4d0ff6e
• 💚 Build #151777 succeeded f0ddec3

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[kibanamachine]

💚 Backport successful

Status	Branch	Result
✅	7.x

This backport PR will be merged automatically after passing CI.