add support for URI variable population based on expressions in HTTP outbound adapters [INT-1349]

[spring-operator]

Mark Fisher opened INT-1349 and commented

For example:

<http:outbound-gateway uri="http://weather/{zipCode}">
    <http:uri-variable key="zipCode" expression="@payload.user.address.zipCode"/>
</http:outbound-gateway>

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Issue Links:

• Add 'value' attribute to the 'uri-variable' sub-element [INT-2463] #6444 Add 'value' attribute to the 'uri-variable' sub-element