Backport of Fix issue with persisting proxy-defaults into release/1.15.x

[dhiaayachi]

Backport

This PR is auto-generated from hashicorp#20481 to be assessed for backporting due to the inclusion of the label backport/1.15.

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The below text is copied from the body of the original PR.

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This resolves an issue introduced in hashicorp#19829 where the proxy-defaults configuration entry with an HTTP protocol cannot be updated after it has been persisted once and a router exists. This occurs because the protocol field is not properly pre-computed before being passed into validation functions and will result in a protocol mis-match error message (the new proxy-defaults will have an assumed protocol of tcp which will conflict with the router's need for http).

This PR hoists the protocol computing logic into the Normalize function of the config entry, which will ensure that it is properly populated prior to the validation function executing.

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Overview of commits

• b5c6c1d - 1b7dbd7