Anthropic module to support setting the base_url and the uri, not only base_url

[ddobrin]

Anthropic module does not allow the user to set both:

1. spring.ai.anthropic.base-url (can be set)
2. spring.ai.anthropic.uri (can not be set, name can be changed)
   It hard-codes the URI to /v1/messages and should be a user-settable value, including an empty String

Similar example: OpenAI module
https://docs.spring.io/spring-ai/reference/api/chat/openai-chat.html#_configuration_properties

Rationale:
If the Anthropic model is deployed in a managed environment, the base URL and URI should be user-settable, allowing also for an empty value for the uri, as the model could be hosted in different managed or self-hosted environments

[ilayaperumalg]

Closing this as complete via #2869