Update terminology in BUILD_DETAIL.md

Created by: JuanitoFatas

This Pull Request updates terminology in BUILD_DETAIL.md.

Allowlist is easier to understand and better terminology.

Original motivation, other community efforts examples:

• https://github.com/rails/rails/pull/33681
• https://github.com/graphiti-api/graphiti/pull/10
• https://github.com/rails/rails/pull/33718
• https://github.com/ruby/psych/pull/378
• https://github.com/ruby/ruby/pull/2008
• https://github.com/ruby/ruby/pull/2009
• https://github.com/rubocop-hq/rubocop/pull/6464
• https://github.com/rubygems/rubygems/pull/2463
• https://github.com/dtao/safe_yaml/pull/93
• https://github.com/rack/rack/pull/1314
• https://github.com/rubocop-hq/rubocop/pull/6466
• https://github.com/rubocop-hq/rubocop/pull/6467
• https://github.com/rspec/rspec-expectations/pull/1083
• https://github.com/rspec/rspec-mocks/pull/1246
• https://github.com/rspec/rspec-support/pull/356
• https://github.com/flavorjones/loofah/pull/158
• https://github.com/pry/pry/pull/1874
• https://github.com/pry/pry/pull/1875