Shrink spec allowlist for cross-database queries

Background

In #337077 (closed), we disallowed any queries that joined between tables in main: and ci: databases. e.g. (SELECT * from projects INNER JOIN ci_builds ON ci_builds.project_id = projects.id is forbidden).

There are of course existing queries that cross databases. These are allowlisted by allowing the specs that produce them, the list is in spec/support/database/cross-join-allowlist.yml.

In some cases, the spec allowlist is probably too broad so we switch to using an alternative allowlist method using allow_cross_joins_across_databases. This also allows us to annotate with the issue link where we will be fixing the cross-database query.

What does this MR do?

Shrink spec allowlist for cross-database queries

Generated from !69037 (closed)

Recent work on adding callsite allowlists (see related MRs in #339299 (closed)) has allowed us to shrink this spec-based allowlist.

Related issue: #339299 (closed)