[Github Audit]: Map github.query_string as a multi-field with a match_only_text field and increase the ignore_above value

### Integration Name

GitHub [packages/github]

### Dataset Name

github.audit

### Integration Version

unrelated

### Agent Version

unrelated

### OS Version and Architecture

unrelated

### User Goal

The field `github.query_string` does not have a explicit mapping, so it is being mapped dynamically, in this case it is being mapped as a `keyword` field with an `ignore_above` set as `1024`.

Since this field may have the full query string for GraphQL requests, it can easily pass the `1024` limit and be marked as `ignored`.

This field should be explicitly mapped with an increase in the `ignore_above` and also have a `match_only_text` multi-field to makes searches easier.

The same may apply to the field `github.filtered_request_body.query` since it will be a copy of `github.query_string` and some users are not removing it.

### Existing Features

The field `github.query_string` is mapped as `keyword` with `ignore_above` set as `1024`

### What did you see?

Fields are being marked as ignored, not being possible to search on them on some events.

In my case 20% of events have the field `github.query_string` marked as ignored.

### Anything else?

_No response_