4.19 vpc conserve mode fix backport

[DaanHoogland]

Description

This PR… backports #10744.

Only new installations of 4.19.x will not have conservemode enabled by default vor VPCs. Upgrades from earlier versions will be alright. In order to make sure conserve mode is enabled for VPC-tiers, either create a clone of the default guestnetwork offering with conservemode enabled or execute the following sql:

-- Re-apply VPC: update default network offering for vpc tier to conserve_mode=1 (#8309)
UPDATE `cloud`.`network_offerings` SET conserve_mode=1 WHERE name='DefaultIsolatedNetworkOfferingForVpcNetworks’;

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)
• build/CI
• test (unit or integration test code)

Feature/Enhancement Scale or Bug Severity

Feature/Enhancement Scale

• Major
• Minor

Bug Severity

• BLOCKER
• Critical
• Major
• Minor
• Trivial

Screenshots (if appropriate):

How Has This Been Tested?

How did you try to break this feature and the system with this change?

[weizhouapache]

code lgtm