Gradle configuration does not allow the use of mirror repos

### Topic

gradle

### Relevant information

The current gradle setup does not allow the injection of mirror repos, which is a common practice in enterprise setups, where access to public repos is prohibited.

It should be possible to tell gradle what maven repo to use, e.g. mavenCentral() when running in default Airbyte CI setup, but when running in more restrictive environment you should be able to set -Dorg.gradle.project.apacheMavenRepositoryUrl. This is then being handled by and if/else statement to handle the injection properly.

From maintainability perspective it would also make sense to separately define a repositories.gradle file with all the repos. And reference this from build.gradle

fyi: This is a reopen of https://github.com/airbytehq/airbyte/issues/64896

Start by locating the Gradle build.gradle repository declarations and review the earlier issue #64896 for context. Separate the repository configuration into repositories.gradle if appropriate, preserving mavenCentral() as the default while allowing org.gradle.project.apacheMavenRepositoryUrl to select a mirror; verify both default and overridden Gradle builds.

索引モデルが issue の本文から書いたものです。