Subpath routing is broken.

https://github.com/google/adk-web/issues/218 describes how can the web-ui be deployed to as subpath, but https://github.com/google/adk-web/blob/03b23e615db45ec912bf75aae1259cafad03c5d6/src/app/core/services/agent.service.ts#L111 does not pick it correctly, because it takes the serverDomain from [here](https://github.com/google/adk-web/blob/03b23e615db45ec912bf75aae1259cafad03c5d6/src/app/core/services/agent.service.ts#L28) which takes the base url from [here](https://github.com/google/adk-web/blob/03b23e615db45ec912bf75aae1259cafad03c5d6/src/utils/url-util.ts#L39)