Fix get assigned entity channels qb

[monrostar]

Description

This fisk is necessary because typeorm does not remove the original table from the from query when creating the qb. In order to do this it was necessary to use manager.

Now a SQL request looking like this

‌SELECT "channel"."channelId" AS "channelId" FROM "public"."product_channels_channel" "channel" WHERE "channel"."productId" = $1

Prev:

SELECT "channel"."channelId" AS "channelId" FROM "public"."asset" "Asset", "public"."asset_channels_channel" "channel" WHERE "channel"."assetId" = $1

Breaking changes

Does this PR include any breaking changes we should be aware of?

• no

Screenshots

Checklist

📌 Always:

• I have set a clear title
• My PR is small and contains a single feature
• I have checked my own PR

👍 Most of the time:

• I have added or updated test cases
• I have updated the README if needed