Buf Contributor License Agreement link is broken

[alexongh]

The link at .github/CONTRIBUTING.md titled Buf's Contributor License Agreement is broken.

Currently, it is linking to the following URL: https://cla-assistant.io/connectrpc/connect-query-es

Which displays the following error:

[perezd]

Thanks for catching that. In fact, this CLA needs to be replaced with our CNCF setup.

[drice-buf]

I'll make the changes once I have the necessary repo permissions.

[drice-buf]

Fixes across all connect repos:

https://github.com/connectrpc/authn-go/pull/15 https://github.com/connectrpc/conformance/pull/900 https://github.com/connectrpc/connect-dart/pull/6 https://github.com/connectrpc/connect-es/pull/1136 https://github.com/connectrpc/connect-go/pull/765 https://github.com/connectrpc/connect-kotlin/pull/298 https://github.com/connectrpc/connect-playwright-es/pull/146 https://github.com/connectrpc/connect-query-es/pull/388 https://github.com/connectrpc/connect-swift/pull/279 https://github.com/connectrpc/connectrpc.com/pull/184 https://github.com/connectrpc/envoy-demo/pull/20 https://github.com/connectrpc/examples-es/pull/1707 https://github.com/connectrpc/examples-go/pull/180 https://github.com/connectrpc/grpchealth-go/pull/70 https://github.com/connectrpc/grpcreflect-go/pull/76 https://github.com/connectrpc/otelconnect-go/pull/178 https://github.com/connectrpc/validate-go/pull/22 https://github.com/connectrpc/vanguard-go/pull/129