Add proper validator log level and handling to "Run rippled as a Validator" docs

[brettmollin]

https://xrpl.org/docs/infrastructure/configuration/server-modes/run-rippled-as-a-validator

@mtrippled has steps for proper validator logging we could add to docs.

Log level at debug

This can be defined as a startup command in rippled.cfg (requires service restart)

[rpc_startup]
{ "command" : "log_level", "severity" : "debug" }

Performance logging

Even more critical since logs will be much larger.
log rotation

Sample of file size with this logging and rotation schedule:

/etc/logrotate.d$ ls -lth /space/rippled/log/
total 26G
-rw-r--r-- 1 rippled rippled 11G Aug 26 16:03 debug.log
-rw-r--r-- 1 rippled rippled 287M Aug 26 16:03 perf.log
-rw-r--r-- 1 rippled rippled 2.1G Aug 26 00:00 debug.log.1.gz
-rw-r--r-- 1 rippled rippled 29M Aug 25 23:59 perf.log.1.gz
-rw-r--r-- 1 rippled rippled 2.2G Aug 25 00:00 debug.log.2.gz
-rw-r--r-- 1 rippled rippled 30M Aug 25 00:00 perf.log.2.gz
-rw-r--r-- 1 rippled rippled 2.1G Aug 24 00:00 debug.log.3.gz
-rw-r--r-- 1 rippled rippled 29M Aug 24 00:00 perf.log.3.gz
-rw-r--r-- 1 rippled rippled 2.0G Aug 23 00:00 debug.log.4.gz
-rw-r--r-- 1 rippled rippled 29M Aug 23 00:00 perf.log.4.gz
-rw-r--r-- 1 rippled rippled 2.0G Aug 22 00:00 debug.log.5.gz
-rw-r--r-- 1 rippled rippled 30M Aug 22 00:00 perf.log.5.gz
-rw-r--r-- 1 rippled rippled 1.9G Aug 21 00:00 debug.log.6.gz
-rw-r--r-- 1 rippled rippled 31M Aug 21 00:00 perf.log.6.gz
-rw-r--r-- 1 rippled rippled 2.1G Aug 20 00:00 debug.log.7.gz
-rw-r--r-- 1 rippled rippled 30M Aug 20 00:00 perf.log.7.gz