[java] [resttemplate] Add support for a bearer token supplier to OAuth based RestTemplate clients

[GregDThomas]

Fixes #19000

Add support for a bearer token supplier to OAuth based RestTemplate clients

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[wandi34]

Is there a reason why this was only added in deprecated RestTemplate? I would really like to see this also in RestClient

[GregDThomas]

I needed it in RestTemplate. I didn't need it in RestClient.