[SEDONA-211] Enforce release managers to use JDK 8

[jiayuasu]

Did you read the Contributor Guide?

• Yes, I have read Contributor Rules and Contributor Development Guide

Is this PR related to a JIRA ticket?

• Yes, the URL of the assoicated JIRA ticket is https://issues.apache.org/jira/browse/SEDONA-211. The PR name follows the format [SEDONA-211] my subject.

What changes were proposed in this PR?

1. Fix a place in BigBufferedImage to make sure the code is compatible among all Java version >=8
2. Add docs to enforce the release manager to use JDK 8

My original thought was to use <release>8</release> in the POM. However, this leads to several issues

• <release>8</release> compiler arg is only available on JDK >=9. We must set multiple POM profiles which only enables this release arg when JDK >=9 is detected on the release manager's environment.
• Given the complexity of current Sedona pom.xml, adding these 2 new profiles prevents Maven from understanding the Pom structure. Therefore, we cannot add these 2 profiles nor set <release>8</release> as default.

Therefore, I added the instruction to the release manager doc to make sure that one must set mvn to JDK 8 when make a formal release.

If your Maven (mvn --version) points to other JDK versions, you must change it to JDK 8. Steps are as follows:

1. Find all Java installed on your machine: /usr/libexec/java_home -V. You should see multiple JDK versions including JDK 8.
2. Run whereis mvn to get the installation location of your Maven. The result is a symlink to the actual location.
3. Open it in the terminal (with sudo if needed). It will be like this

#!/bin/bash
JAVA_HOME="${JAVA_HOME:-$(/usr/libexec/java_home)}" exec "/usr/local/Cellar/maven/3.6.3/libexec/bin/mvn" "$@"

4. Change JAVA_HOME:-$(/usr/libexec/java_home)} to JAVA_HOME:-$(/usr/libexec/java_home -v 1.8)}. The resulting content will be like this:

#!/bin/bash
JAVA_HOME="${JAVA_HOME:-$(/usr/libexec/java_home -v 1.8)}" exec "/usr/local/Cellar/maven/3.6.3/libexec/bin/mvn" "$@"

5. Run mvn --version again. It should now point to JDK 8.

How was this patch tested?

Did this PR include necessary documentation updates?

• No, this PR does not affect any public API so no need to change the docs.