Added /validate endpoint and modified mcp-publish so that all validation happens there#896

BobDickinson wants to merge 2 commits intomodelcontextprotocol:mainmodelcontextprotocol/registry:mainfrom

BobDickinson:publish-validation-and-validate-endpointBobDickinson/registry:publish-validation-and-validate-endpointCopy head branch name to clipboard