## Description
Following d6c6351c7f0b241578121d459943fdf2b305571e, the `ir.rule` related to discuss channels got more elaborated, with more subqueries. When loading an `avatar_128`, in an override of `_find_record_check_access`, a repetitive domain with an `any` operator on the same left leaf. This repetitive domain + the new `ir.rule` lead to a bad postgres plan, leading to a perf regression.

## Fix
We add an `auto_join=True` on `parent_channel_id` to avoid doing an additional nested sub-query coming from the `ir.rule`. This change is safe, as the comodel is the same model as the current one, and an user that has access to a subchannel, should probably already have access to its parent channel.
The other improvement is an optimistic early `super()` call, which should not raise any issue for internal employees, who already should have access to the avatar. In case of an access violation, we fallback on the previous behaviour.

## Benchmark
On a large database, loading an `avatar_128`, cache disabled in browser (simulating a first load) for an internal non-privileged user.

|                      | Timings   |
|----------------------|-----------|
| Before               | 300~400ms |
| `auto_join=True`     | 20~25ms   |
| + `super()` shortcut | 13~23ms   |

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