Extract uploader information into seperate DB table out of stream table

[XiangRongLin]

Checklist

• I am using the latest version - x.xx.x
• I checked, but didn't find any duplicates (open OR closed) of this issue in the repo.
• I have read the contribution guidelines given at https://github.com/TeamNewPipe/NewPipe/blob/HEAD/.github/CONTRIBUTING.md.

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NewPipe/app/src/main/java/org/schabi/newpipe/database/stream/model/StreamEntity.kt

Lines 49 to 50 in 21bcade

	@ColumnInfo(name = STREAM_UPLOADER_URL)
	var uploaderUrl: String? = null,

The uploader name is saved inside the streams table. This causes it to be duplicated for each occurence.
With the addition of the url of the uploader (#6919) it makes sense to extract both fields into a seperate table for uploaders and reference it.

The uploader names must to be migrated and the urls should ideally be migrated.

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@ktprograms Am i correct in my assesment, that in theory not migrating the url, would only cause some loading extra loading times?

[ktprograms]

The uploader url isn't currently in the database. So newly saved videos will insert the url, and for old videos the code fetches it using the extractor, then saves it to the database for the next time.