database: Add versions.num_no_build column

[Turbo87]

This shall be filled by the following SQL script:

update versions
    set num_no_build = split_part(num, '+', 1);

with duplicates as (
    -- find all versions that have the same `crate_id` and `unique_num`
    select crate_id, num_no_build, array_agg(num ORDER BY id) as nums
    from versions
    group by crate_id, num_no_build
    having count(*) > 1
),
duplicates_to_update as (
    -- for each group of duplicates, update all versions except the one that
    -- doesn't have "build metadata", or the first one that was published if
    -- all versions have "build metadata"
    select crate_id, num_no_build, unnest(case when array_position(nums, num_no_build) IS NOT NULL then array_remove(nums, num_no_build) else nums[2:] end) as num
    from duplicates
)
update versions
    set num_no_build = duplicates_to_update.num
    from duplicates_to_update
    where versions.crate_id = duplicates_to_update.crate_id
    and versions.num = duplicates_to_update.num;

The script takes a few seconds to complete, so this should not be added to the database schema migration script, since it would block the API server from booting.

---

This PR was extracted from #9756, because it needs to be deploy separately from the other migrations in that PR.

[codecov]

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