Always store the termdict indices in the hotcache.

[fulmicoton]

Always store the termdict indices in the hotcache.

Before it could be skipped if it was greater than 10mb,
but Quickwit does not work at all if it not there.

Such size was uncommon and due to a misconfiguration.
We are mitigating the size problem independently.

Closes #1366

I verified manually that the bug described in #1366 was sovled.

 cargo run --release  -- index search --index hackernews_5 --query "Ambulance"
    Finished release [optimized] target(s) in 0.27s
     Running `target/release/quickwit index search --index hackernews_5 --query Ambulance`
{
  "num_hits": 9,
  "hits": [
    {
      "id": 16203439,
      "text": "Be the real super hero not by the super powers but by the deeds that matter, save the life of the Civilians in the city in the most realistic Rescue Simulation Games of time, Ambulance Rescue & Helicopter Heroes.",
      "title": "Ambulance Rescue and Helicopter Heroes",
      "type": "story"
    },
    {