minor #38413 [HttpClient] change piority of RetryableHttpClient (jderusse)

This PR was merged into the 5.2-dev branch.

Discussion
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[HttpClient] change piority of RetryableHttpClient

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | /
| License       | MIT
| Doc PR        | /

This make the RetryableHttpClient decorated the TraceableHttpClient.
User will be able to check content of each sub-request

Commits
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9568d437 Change priority of RetryableHttpClient