fix webhook form for Ticket approvals

[SebSept]

Checklist before requesting a review

Please delete options that are not relevant.

• I have read the CONTRIBUTING document.
• I have performed a self-review of my code.

I'm not sure of the array value to use as key value, I used schema_name, maybe it's itemtype

[cconard96]

This fix doesn't seem complete yet as there is at least one other itemtype that triggers an error in getMonacoSuggestions.

You may add the following test to at least ensure all itemtypes in the dropown get at least some suggestions without error:

    public function testGetMonacoSuggestions()
    {
        $itemtypes = Webhook::getItemtypesDropdownValues();
        $failed_itemtypes = [];
        foreach ($itemtypes as $types) {
            $this->assertIsArray($types);
            foreach ($types as $itemtype => $label) {
                try {
                    $suggestions = Webhook::getMonacoSuggestions($itemtype);
                    $this->assertNotEmpty($suggestions);
                } catch (\Throwable $e) {
                    $failed_itemtypes[$itemtype] = [
                        'error' => $e->getMessage(),
                        'trace' => $e->getTraceAsString()
                    ];
                }
            }
        }
        $this->assertEmpty($failed_itemtypes, print_r($failed_itemtypes, true));
    }

[SebSept]

I fixed other undefined index errors & added a test.
It reveals that a Missing suggestions for ITILFollowup that probably needs to be fixed (or ignored in the test). (so ci is red)

[cconard96]

I think I may take this over and rewrite the integration with the HLAPI to reduce the complexity and rely more on static data instead of guesses. The identification of parent itemtypes does not seem reliable as-is.

[SebSept]

Relying on object not arrays is a good option.
Will you fix the failing test ? @cconard96 (it will take a long for me, because of the time to find why there is a missing suggestion for an ITILFollowUp.)

[cedric-anne]

replaced by #21181