test: add mixed version and rolling upgrade CCIP tests

[nvsriram]

This PR adds:

1. Mixed version test: the baseline image to bootstrap and even-indexed plugin nodes, and the PR image to odd-indexed plugin nodes. It then sends a message to verify compatibility.
2. Rolling upgrade test: all nodes start on baseline image and get upgraded one-by-one. A message is sent between each upgrade to verify upgrade compatibility.

[github-actions]

CORA - Pending Reviewers

Codeowners Entry	Overall	Num Files	Owners
/.github/**	🚫	2	@smartcontractkit/devex-cicd, @smartcontractkit/devex-tooling, @smartcontractkit/core

Legend: ✅ Approved | ❌ Changes Requested | 💬 Commented | 🚫 Dismissed | ⏳ Pending | ❓ Unknown

For more details, see the full review summary.

[github-actions]

✅ No conflicts with other open PRs targeting develop

[trunk-io]

   

View Full Report ↗︎ ⋅ Docs

[nvsriram]

The actual rollout test was not being run with the CI job (it was being skipped) so I manually triggered the workflows to verify:

• Trivial workflow run that passes:
  https://github.com/smartcontractkit/chainlink/actions/runs/33419754115
• Negative test case workflow run based on test: negative rollout test #23589 that fails: https://github.com/smartcontractkit/chainlink/actions/runs/33422354286