Fixes #39336 - Batch taxonomy subtree lookups to avoid N+1 queries

[adamruzicka]

Heavily inspired by https://community.theforeman.org/t/bug-orgs-and-locs-job-templates-are-broken-in-3-18-probably-3-17-as-well/46388/15

When a user belongs to many organizations, authorization performed 1+N SQL queries per taxonomy type to resolve subtree IDs (one subtree_ids pluck per organization). This patch replaces the per-taxonomy loop with a single batched query using OR conditions on the ancestry column.

Alternatives would be using recursive CTEs to let postgres walk the subtrees with a single query, but CTEs are still somewhat uncommon in rails lands.

The problem grows purely with the number of taxonomies assigned to the user. Here I have a user with 337 organizations and 1801 locations.

Before

# time curl --silent -q -u $username:$password -k https://$(hostname -f)/api/v2/job_templates | jq '.total'
79

real	0m12.970s
user	0m0.016s
sys	0m0.012s

After

# time curl --silent -q -u $username:$password -k https://$(hostname -f)/api/v2/job_templates | jq '.total'
79

real	0m4.527s
user	0m0.015s
sys	0m0.014s

[adamruzicka]

With the ignored taxonomies commit:

# time curl --silent -q -u $username:$password -k https://$(hostname -f)/api/v2/job_templates | jq '.total'
79

real    0m1.884s
user    0m0.013s
sys     0m0.012s

[adamruzicka]

# time curl --silent -q -u $username:$password -k https://$(hostname -f)/api/v2/hosts | jq '.total'
1

real    0m25.790s
user    0m0.015s
sys     0m0.014s

# time curl --silent -q -u $username:$password -k https://$(hostname -f)/api/v2/hosts | jq '.total'
1

real    0m4.581s
user    0m0.016s
sys     0m0.011s