Update baseRetryPolicy to handle 409 statusCode.

[Dpk89364]

• 429 Too Many Requests and 409 Concurrency Conflict are recoverable errors.
• In the case of a 429, the server sometimes includes a Retry-After response header to indicate when it will be available to start processing requests from the client.
• In the case of a 409, if there are more than one concurrent request, the server is unable to serve that request. In that case, we can use an exponential backoff strategy (1 sec, 2 sec, 4 sec, 8 sec, 16 sec…).

[hashicorp-cla-app]

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