This commit replaces the WebClient.filter method with
WebClient.Builder.filter. The reason for this change is that filters
added via WebClient.filter would be applied in the opposite order of
their declaration, due to the compositional nature of the method,
combined with the immutable nature of the WebClient.
WebClient.Builder.filter does keep the order of the filters, as
registered.
Furthermore, this commit introduces a WebClient.mutate() method,
returning a WebClient.Builder. This method allow to add/remove filters
and other defaults from a given WebClient.
Issue: SPR-15657
Add WebClient.Builder.addFilter
Add Consumer-based headers and cookies methods to builders.
Add WebClient.mutate
4a0597d612