Reduce the allocated IP for Cluster and Services

What does this MR do?

This MR aims to reduce the allocated space for cluster and services since on GitLab's internal GCP project used for demos and testing, we often see clusters failing to be created due to lack of space.

@tkuah suggested that we could try to reduce the IP space once we have VPC-Native clusters setup: #25925 (comment 215583091)

As per the 2019-10-23 APAC/EMEA Configure:Orchestration team meeting, we've decided to reduce the default allocated IP range from /14 (262144 IPs) to /16 (65536 IPs).

Screenshots

Manual QA

Installed via GitLab integration.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team