[gssapi/gssproxy] 358ab1: KRB5_TRACE documentation for gssproxy

[jacobshivers]

Branch: refs/heads/main
  Home:   https://github.com/gssapi/gssproxy
  Commit: 358ab121cd72092faf159c9f1a56fc6382920df2
      https://github.com/gssapi/gssproxy/commit/358ab121cd72092faf159c9f1a56fc6382...
  Author: Jacob Shivers 
  Date:   2022-03-08 (Tue, 08 Mar 2022)

Changed paths:
    A docs/KRB5_TRACE.md
    M man/gssproxy.conf.5.xml

Log Message:
  -----------
  KRB5_TRACE documentation for gssproxy

Added KRB5_TRACE.md to provide a brief overview on how to enable low
level Kerberos tracing below gssapi via KRB5_TRACE.

Updated gssproxy.conf man page to cite newly added doc when mentioning
KRB5_TRACE behavior.

Signed-off-by: Jacob Shivers