[Feature] Add support for case insensitive comparison in filter

When using filters with DAB GraphQL, it relies on case sensitive filtering with various operators such as `eq`, `neq`, `contains` etc. I would like to be able to do case insensitive comparison when using filters.

We could add support for a caseInsensitive operator along the filter operator to support this usecase.
For e.e.g
```
{
publicholis (filter: {
holidayName: {
eq: "Ascension"
caseInsensitive: true
}
}) {
items {
holidayName
countryOrRegion
}
}
}
```