Move busybox image settings to global

• Deprecates init.image, init.tag and init.pullPolicy in favor of init.image.repository, init.image.tag, and init.image.pullPolicy
• Adds global.busybox.image.repository and global.busybox.image.tag settings to handle all init container images
  • Chart-local values for init.image.repository and init.image.tag, if specified, gets priority over global ones.

Closes: #1656 (closed)