Upgrade HAProxy from 2.6.14 to remedy two CVEs

[avo-sepp]

Summary

HAProxy for ArgoCD HA was last updated June 14, 2023 to 2.6.14. Since that release there are two new CVEs categorized as High for that release.

• CVE-2023-40225 fixed in 2.6.15
• CVE-2023-45539 fixed in 2.8.2

Motivation

These are showing up as cyber security vulnerabilities in our scanning tools. We bumped HAProxy to 2.9.7 on our production Argo and are test-piloting the dependency change for issues.

Proposal

I've prepared a draft PR to version bump HAProxy from 2.6.14 to 2.9.7. After a period of testing on our Argo I can publish the draft PR. I selected 2.9.7 because it's latest stable. However, 2.8 is LTS and contains the required CVE fixes. If the community prefers, we could test 2.8-alpine and automatically track patch updates to the LTS version of HAProxy. Or stay on 2.9-alpine and track patches to the later version, skipping LTS.

See #18158