AvaticaCommonsHttpClientImpl client needs to set user-token on HttpClientContext before sending the request

One of the Avatica client implementations, AvaticaCommonsHttpClientImpl, uses a PoolingHttpClientConnectionManager. When using mutual authentication on the client pool, we need to ensure that we are setting a user-token on the HttpClientContext, otherwise it ends up creating a new connection everytime and not reusing it. See:  https://hc.apache.org/httpcomponents-client-ga/tutorial/html/advanced.html for more details

This results in significant perf degradation since every new connection tries to complete a SSL handshake (which is expensive)

See: https://stackoverflow.com/questions/548029/how-much-overhead-does-ssl-impose