Add some errors and validation for group_rules and coroutine_stack_size with ldap

[aidekqz]

group_rules:

Received signal SIGSEGV if group_rule parameters not defined

database "db1" {
    group "group1" {
        authentication "md5"
        auth_query "SELECT usename, passwd FROM pg_shadow WHERE usename=$1"
        auth_query_user "postgres"
        auth_query_db "postgres"
        storage "postgres_server"
        pool "transaction"
        # group_query "SELECT rolname FROM pg_roles WHERE pg_has_role(rolname, 'group1', 'member')"
        # group_query_user "postgres"
        # group_query_db "postgres"
    }
}

Thread 4 "system" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff70ae640 (LWP 57430)]
__strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:74
74      ../sysdeps/x86_64/multiarch/strlen-avx2.S: No such file or directory.
(gdb) bt
#0  __strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:74
#1  0x0000555555563a8d in od_rules_group_checker_run (arg=0x7fffe00078d0) at /odyssey/sources/rules.c:213
#2  0x00005555555bec49 in mm_scheduler_main (arg=0x7fffe00078f0) at /odyssey/build/third_party/machinarium/sources/scheduler.c:17
#3  0x00005555555c11ff in mm_context_runner () at /odyssey/build/third_party/machinarium/sources/context.c:28
#4  0x0000000000000000 in ?? ()

coroutine_stack_size

coroutine_stack_size must be greater than 16
https://github.com/yandex/odyssey/blob/a0f5ec5d4d49077f322f49d900c3c598bc1a9da2/documentation/configuration.md#coroutine_stack_size-integer