Required environment variable matching for claim precedence

[iwarapter]

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As part of #22 I have had a (very rough) go at supporting required environment variables for claims.

I have outstanding issue on tests with missing descriptor java.lang.AssertionError: class java.lang.String is missing its descriptor in public final java.util.List io.jenkins.plugins.oidc_provider.config.ClaimTemplate.requiredEnvVars. See https://www.jenkins.io/redirect/developer/class-is-missing-descriptor not sure how to solve this for List of String.