Add speed_note_count to docs

[HonKLam]

Resolves #10345

API call for BeatmapDifficultyAttributes looks like this (in osu):

So I added the missing speed_note_count to docs and it looks like this now:

I also checked the other gamemodes and found some things off:

Taiko

API

Docs

(peak_difficulty vs approach_rate)

Mania

API

Docs

(score_multiplier just missing in general?)

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Is this intended? Otherwise I can offer to fix it in the docs.

[notbakaneko]

BeatmapDifficultyAttributes depends on the output of osu-beatmap-difficulty-lookup-cache which may change and is better documented else where, in my opinion.

[HonKLam]

and is better documented else where, in my opinion

If BeatmapDifficultyAttributes should not be documented in osu docs, but can be requested via API, where should it be documented then?

Could also put in a note in docs that states that BeatmapDifficultyAttributes is subject to change, but that applies to every endpoint or output, doesn't it?

[nanaya]

If BeatmapDifficultyAttributes should not be documented in osu docs, but can be requested via API, where should it be documented then?

the linked project which the endpoint proxies to

Could also put in a note in docs that states that BeatmapDifficultyAttributes is subject to change, but that applies to every endpoint or output, doesn't it?

the code and documentation for other endpoints are in the same repository whereas this one the code is in another castle

[HonKLam]

the code and documentation for other endpoints are in the same repository whereas this one the code is in another castle

I will leave it to the other castle then to update the docs if it's more fitting there. If it happens, maybe put a note in osu-web docs that refers to it?

Feel free to close PR or keep it open as a reminder