feat(migrate): `regexManagers` -> `customManagers` (#24451)

docs/usage/configuration-options.md

docs/usage/getting-started/use-cases.md

docs/usage/reading-list.md

...ge/user-stories/maintaining-aur-packages-with-renovate.md

docs/usage/user-stories/swissquote.md

lib/config/__snapshots__/migration.spec.ts.snap

lib/config/__snapshots__/validation.spec.ts.snap

lib/config/migration.spec.ts

...onfig/migrations/custom/custom-managers-migration.spec.ts

lib/config/migrations/custom/custom-managers-migration.ts

lib/config/migrations/migrations-service.ts

lib/config/options/index.ts

lib/config/presets/internal/regex-managers.spec.ts

lib/config/presets/internal/regex-managers.ts

lib/config/types.ts

lib/config/validation.spec.ts

lib/config/validation.ts

lib/modules/datasource/aws-machine-image/readme.md

lib/modules/datasource/aws-rds/readme.md

lib/modules/datasource/custom/readme.md