Docs: add Logging.BelowMinLevel and Logging.AboveMaxLevel to the manual page for the Logging stdlib

[DilumAluthge]

According to the source code file, Logging.BelowMinLevel and Logging.AboveMaxLevel are already part of the public API of the Logging stdlib:

julia/stdlib/Logging/src/Logging.jl

Lines 85 to 91 in c8ca350

	# The following are also part of the public API, but not exported:
	#
	# 1. Log levels:
	# BelowMinLevel, Debug, Info, Warn, Error, AboveMaxLevel,
	#
	# 2. AbstractLogger message related functions:
	# handle_message, shouldlog, min_enabled_level, catch_exceptions,

Additionally, Logging currently exports BelowMinLevel and AboveMaxLevel:

julia/stdlib/Logging/src/Logging.jl

Lines 61 to 81 in c8ca350

	export
	AbstractLogger,
	LogLevel,
	NullLogger,
	@debug,
	@info,
	@warn,
	@error,
	@logmsg,
	with_logger,
	current_logger,
	global_logger,
	disable_logging,
	SimpleLogger,
	ConsoleLogger,
	BelowMinLevel,
	Debug,
	Info,
	Warn,
	Error,
	AboveMaxLevel

However, Logging.BelowMinLevel and Logging.AboveMaxLevel are not currently in the manual.

This PR adds them to the manual.

[ericphanson]

imo it would be helpful to have a more descriptive docstring; e.g. what are these for? how should they be used?

[DilumAluthge]

Yeah, I think that would be good. I'm not sure what the intended usage is. I've been using BelowMinLevel in Logging.disable_logging(Logging.BelowMinLevel), which I use as a workaround for #52234.

@c42f Could you weigh in on the intended usage of BelowMinLevel and AboveMaxLevel?

[vtjnash]

It looks like none of the others have a useful description either, so this seems to fit in

[DilumAluthge]

Bump @c42f

[fingolfin]

It would be great if @c42f could chime in, but IMHO even without that this is an improvement (yeah maybe it could be even better, but what can't be...)