Split ElicitationMcpTasksCapability into server and client versions

[halter73]

Given that servers and clients can only support distinct RequestMcpTasksCapabilities, tasks.requests.tools.call for servers, and tasks.requests.sampling.createMessage and tasks.requests.elicitation.create for servers, would it make sense to split McpTasksCapability into ClientMcpTasksCapability and ServerMcpTasksCapability?

Originally posted by @halter73 in #1170 (comment)