fix(apidom-ls): fix OAS example value/externalValue rule

[frantuma]

fixes #2141, updating #2146

the following function is better suited for such cases (check for absence of specific field)

linterFunction: 'missingFields',
linterParams: [['value']],

the following places the marker on the value key (not on the parent)

  markerTarget: 'value',

also added test

[char0n]

If the test is stuck, it means that it is failing - there is something wrong with the way the tests are written as some failing tests make the entire suite loop indefinitely.