client, improvement on Headers class property definitions

[weidongxu-microsoft]

Headers class like below would trigger some "EnforceFinalFields" error in check-style
https://github.com/Azure/azure-sdk-for-java/blob/e621a3c9dba7853280bd5432d873b7ea94fb88b8/sdk/avs/azure-resourcemanager-avs/src/main/java/com/azure/resourcemanager/avs/models/PrivateCloudsUpdateHeaders.java

error is

 src/main/java/com/azure/resourcemanager/avs/models/PlacementPoliciesUpdateHeaders.java(19,5): error :  src/main/java/com/azure/resourcemanager/avs/models/PlacementPoliciesUpdateHeaders.java:[19,5] (extension) EnforceFinalFields: Field "retryAfter" is only assigned in constructor and it is not final. You should consider making the field final, or suppressing the warning.

https://github.com/Azure/azure-sdk-for-java/pull/40479/checks?check_run_id=27728266899

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There is some nuance on the property
private String location; seems can be directly a final property.
However, private Integer retryAfter; cannot be final, unless a minor change in code e.g.

    this.retryAfter = retryAfter != null ? Integer.parseInt(retryAfter) : null;