[chore] update memory limits

[puckpuck]

Changes

Updates memory limits for the following services:

flagd: 50M -> 75M
flagdui: 150M -> 75M
loadgenerator: 1G -> 1500M

These changes are based on long-term testing I have been running in EKS. Even with the significant increase for the loadgenerator service, we are still under the 6G minimum requirement listed in the docs. The total of all services is now 5400MB.

Merge Requirements

For new features contributions, please make sure you have completed the following
essential items:

• CHANGELOG.md updated to document new feature additions
• Appropriate documentation updates in the docs
• Appropriate Helm chart updates in the helm-charts

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.