Add check_multi

[lgmu]

By default 'CheckMulti' is enabled, but you can disable it in the '[/modules]' section of the snclient_local.ini.
You can also set a limit for the number of checks that can be executed in the '[/settings/check/multi]' section
of the snclient_local.ini.

When using the inline mode, you can only use available commands (run 'check_index' to get a full list).

You can also define custom check sections in the config file, for example:
[/settings/check/multi/mycheck]
check_process process=123
check_process process=345

This can be executed with 'check_multi "config=mycheck"'.

It's also possible to use custom scripts in the config section, for example:
[/settings/check/multi/myscript]
/path/to/plugin1
/path/to/plugin2
/path/to/plugin3

This can be executed with 'check_multi "config=myscript"'.

---

Examples: 

check_multi "check=check_process 'process=firefox'" "check=check_memory 'crit=used_pct gt 80%'"
OK - 2 plugins checked, 2 ok | 'check_process::count'=1;;;0 'check_process::rss'=258686976B;;;0 ...
[ 1] check_process OK - all 1 processes are ok.
[ 2] check_memory OK - physical = 12.22 GiB/16.00 GiB (76.4%), swap = 1.95 GiB/3.00 GiB (65.0%)

You can define warning/critical conditions based on the number of checks in a certain state (see attributes below):

check_multi "check=check_dummy 0 'OK'" "check=check_dummy 1 'WARNING'" "critical=problem_count gt 0"
CRITICAL - 2 plugins checked: 1 ok, 1 warning, 0 critical, 0 unknown
[ 1] check_dummy OK
[ 2] check_dummy WARNING

[lgmu]

ToDo:

• bugfix IF ELSE Conditions in top-syntax
• add advanced example to docs

check_multi "check=check_dummy 2 'CRITICAL'" "check=check_dummy 3 'UNKNOWN'" "top-syntax={{ IF ok_count gt 0 }}OK - %(ok_count)/%(count) checks are OK {{ ELSE }}CRITICAL - all checks failed{{ END }}"
OK - 0/2 checks are OK
[ 1] check_dummy CRITICAL
[ 2] check_dummy UNKNOWN

[lgmu]

Discuss with @sni why it was 0 in the first place

[inqrphl]

This test is passing without changes on windows for the latest main commit f9a22ac

the file MD5 is 3687C5D7106484CD61CDE867A2A999FA so raising critical is correct.

[lgmu]

yea but problem_count is 0, while it should be 1.
CRITICAL is still expected, nothing has changed there