[maven-plugin] fix strictSpec parameter

[jmini]

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Description of the PR

Introduced with #2783, the strictSpec parameter causes the an error in the 4.0.1 maven plugin:

[ERROR] Failed to execute goal org.openapitools:openapi-generator-maven-plugin:4.0.1:generate (generate-client-code): Unable to parse configuration of mojo org.openapitools:openapi-generator-maven-plugin:4.0.1:generate for parameter strictSpec: Cannot find 'strictSpec' in class org.openapitools.codegen.plugin.CodeGenMojo -> [Help 1]

This PR is about to fix it.

[wing328]

LGTM

[jimschubert]

@jmini

@wing328 and I were discussing this fix in chat. I was wondering, would you mind if we change the property to strictSpec so we aren't supporting two aliases for the same setting in Maven, Gradle, and CLI?

[jmini]

Yes as discussed in Gitter a solution might be to revert the change made here with the alias parameter but to rename:

private Boolean strictSpecBehavior;

To:

private Boolean strictSpec;

This will have the same effect.