Remove `ProjectAuthorization.insert_authorizations` method

What does this MR do and why?

This MR does multiple things:

• Removes the ProjectAuthorization.insert_authorizations method - because this method acts the same way as the Rails's built-in insert_all method, so there is no need to keep and maintain another method that does the same thing.

Query generated on ProjectAuthorization.insert_all

ProjectAuthorization.insert_all([{user_id: 1, project_id: 1, access_level: 20}, {user_id: 108, project_id:48, access_level: 20}])

INSERT INTO "project_authorizations" ("user_id","project_id","access_level") VALUES (1, 1, 20), (108, 48, 20) ON CONFLICT ("user_id","project_id","access_level") DO NOTHING RETURNING "user_id","project_id","access_level"

Query generated on ProjectAuthorization.insert_authorizations

ProjectAuthorization.insert_authorizations([[108, 47, 20]])

INSERT INTO "project_authorizations" ("user_id","project_id","access_level") VALUES (108, 47, 20) ON CONFLICT DO NOTHING

We can see that the query differs slightly only in the ON CONFLICT DO NOTHING part, but the unique key on project_authorizations table is on (user_id, project_id, access_level) alone, so being explicit about ON CONFLICT ("user_id","project_id","access_level") DO NOTHING and just mentioning ON CONFLICT DO NOTHING means the same thing on this table. So we are safe to use insert_all in place of insert_authorizations.

• insert_authorizations however, allowed to bulk insert records in batches of 1000 for performance, so we have now introduced insert_all_in_batches that simply calls insert_all internally, for each batch so that insert_authorizations and insert_all_in_batches behave exactly the same way.

• And now that we have insert_all_in_batches, which does batched inserts, we can replace usages of both ProjectAuthorization.insert_authorizations and ProjectAuthorization.insert_all with ProjectAuthorization.insert_all_in_batches

(no changelog added as this is only a refactor in the internal implementation detail)

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