Etar: gradle: Refactor gradle configuration

- Sync with latest templates
- Migrate to plugins & lint block globally
- Switch to new dependency and plugins management
- Split external dependency configurations
- Switch to new Sdk version properties
- Bump gradle version to latest
- Enable java 11 lang features

Signed-off-by: Aayush Gupta <aayushgupta219@gmail.com>
Change-Id: Ic915bcca1b97cb7fac21364f8876302ede26d550