[Java] Refactor webClient generator to use URI templates to capture correct metrics

Created by: atsharp

Spring supports automatic instrumentation of WebClient and RestTemplate to capture metrics when using injected clients. When instrumenting these HTTP clients, a URI template must be provided to properly group parameterized HTTP requests. For example, given a URI /resources/{id}, metrics should be captured under /resources/{id} instead of/resources/1234/resources/4321/etc.

Currently, the OpenAPI generated RestTemplate clients use RestTemplate.getUriTemplateHandler, which can capture URI templates and resolve metrics appropriately. However, WebClient based templates render paths as Strings directly, which erases the template and results in incorrect metric instrumentation:

String path = UriComponentsBuilder.fromPath("{{{path}}}"){{#hasPathParams}}.buildAndExpand(uriVariables){{/hasPathParams}}{{^hasPathParams}}.build(){{/hasPathParams}}.toUriString();

Refactoring the WebClient generated clients to use WebClient.UriSpec.uri(String, Map<String, Object> will capture URI templates and enable appropriate metric collection.

Note that the URI string provided to UriSpec.uri(String, Map) is rendered as a template using UriComponentsBuilder.encode which was introduced in spring-webflux 5.0.8.RELEASE, and thus, requires a minor version increase.

Note that this approach is similar to that of 4299 but is less invasive.

CC: @bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog

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