required by https://github.com/questdb/questdb-enterprise/pull/439 and questdb/ui#291

Adds two new columns to the output of wal_tables(): errorTag, errorMessage
These columns are populated only if the table is suspended.
They help to identify the reason of the table suspension.

errorMessage - the error message logged by QuestDB
errorTag - identifies the type of error, such as DISK FULL or TOO MANY OPEN FILES

The error tag will help the Web Console to direct the user to a page with instructions how to resolve the issue.

Also adds a new endpoint: /warnings.
This returns with a json object containing server configuration issues.
The web console calls this on every reload, and displays the warnings.

Currently we are checking for 3 configuration issues: UNSUPPORTED FILE SYSTEM, TOO MANY OPEN FILES and OUT OF MMAP AREAS.

Also fixes error codes in CairoException.
The same error codes were used for different errors.

Also adds a new SQL command to be able to suspend tables.
Optionally an error code/tag and error message can be specified.
The command has been added primarily to help testing.
Examples:

ALTER TABLE tab1 SUSPEND WAL;
ALTER TABLE tab1 SUSPEND WAL WITH 24, 'test error';
ALTER TABLE tab1 SUSPEND WAL WITH 'DISK FULL', 'test error';

Also adds a new SQL function to simulate warnings.
Examples:

select simulate_warnings('UNSUPPORTED FILE SYSTEM', 'Unsupported file system [dir=/questdb/path/dbRoot, magic=0x6400A468]');
select simulate_warnings('TOO MANY OPEN FILES', 'fs.file-max limit is too low [current=1024, recommended=1048576]');
select simulate_warnings('OUT OF MMAP AREAS', 'vm.max_map_count limit is too low [current=4096, recommended=1048576]');

Web console should be reloaded after the function is executed, and the warning should appear.
Warnings accumulate, so you should see as many warnings as commands issued.
You can clear the warnings by running:

select simulate_warnings('', '');