a client site web app which lets a user check all the boxes for all of the possible fields and it outputs a log-format line

inspired by:https://matduggan.com/were-all-doing-metrics-wrong/

1. MVP: json output
2. text output with ordered field selection

TODO: support sample fetch vars, especially fc_err, ssl_fc_err, ssl_c_err, ssl_c_ca_err, ssl_fc_is_resumed, ssl_fc_sni