[SPARK-30944][BUILD] Update URL for Google Cloud Storage mirror of Maven Central

### What changes were proposed in this pull request?

This PR is a followup to apache#27307: per https://travis-ci.community/t/maven-builds-that-use-the-gcs-maven-central-mirror-should-update-their-paths/5926, the Google Cloud Storage mirror of Maven Central has updated its URLs: the new paths are updated more frequently. The new paths are listed on https://storage-download.googleapis.com/maven-central/index.html

This patch updates our build files to use these new URLs.

### Does this PR introduce any user-facing change?

No.

### How was this patch tested?

Existing build + tests.

Closes apache#27688 from JoshRosen/update-gcs-mirror-url.

Authored-by: Josh Rosen <[email protected]>
Signed-off-by: HyukjinKwon <[email protected]>

Author: JoshRosen

pom.xml

@@ -253,7 +253,7 @@
         See https://storage-download.googleapis.com/maven-central/index.html
       -->
       <name>GCS Maven Central mirror</name>
-      <url>https://maven-central.storage-download.googleapis.com/repos/central/data/</url>
+      <url>https://maven-central.storage-download.googleapis.com/maven2/</url>
       <releases>
         <enabled>true</enabled>
       </releases>
@@ -284,7 +284,7 @@
         See https://storage-download.googleapis.com/maven-central/index.html
       -->
       <name>GCS Maven Central mirror</name>
-      <url>https://maven-central.storage-download.googleapis.com/repos/central/data/</url>
+      <url>https://maven-central.storage-download.googleapis.com/maven2/</url>
       <releases>
         <enabled>true</enabled>
       </releases>

project/SparkBuild.scala

@@ -226,7 +226,7 @@ object SparkBuild extends PomBuild {
     resolvers := Seq(
       // Google Mirror of Maven Central, placed first so that it's used instead of flaky Maven Central.
       // See https://storage-download.googleapis.com/maven-central/index.html for more info.
-      "gcs-maven-central-mirror" at "https://maven-central.storage-download.googleapis.com/repos/central/data/",
+      "gcs-maven-central-mirror" at "https://maven-central.storage-download.googleapis.com/maven2/",
       DefaultMavenRepository,
       Resolver.mavenLocal,
       Resolver.file("local", file(Path.userHome.absolutePath + "/.ivy2/local"))(Resolver.ivyStylePatterns)

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -2136,7 +2136,7 @@ object SQLConf {
         "if the default Maven Central repo is unreachable.")
       .stringConf
       .createWithDefault(
-        "https://maven-central.storage-download.googleapis.com/repos/central/data/")
+        "https://maven-central.storage-download.googleapis.com/maven2/")
 
   val LEGACY_FROM_DAYTIME_STRING =
     buildConf("spark.sql.legacy.fromDayTimeString.enabled")