Motivation:

Some users are having issues with using Armeria as a Java 9 module
because:

- Armeria core JAR contains `module-info.class` from Bouncy Castle,
  which should be removed during the shading process.
- Armeria doesn't define module metadata at all

Modifications:

- Updated `gradle-scripts` to exclude `module-info.class` while shading.
  - This removes Bouncy Castle's `module-info.class` from the final JAR,
    fixing the issue mentioned in the previous section.
- Updated `gradle-scripts` to auto-inject the `Automatic-Module-Name`
  property into `META-INF/MANIFEST.MF` so that JVM auto-generates the
  module metadata.
- Miscellaneous:
  - Overwrote the `Created-By` property in `META-INF/MANIFEST.MF` so
    that the manifest file's content doesn't change depending on JDK
    version.

Result:

- (new feature) Armeria JARs are now Java modules.

Co-authored-by: minux <songmw725@gmail.com>