feat(appset): Add new strategies to merge generator

[joshfrench]

PR #16080 is abandoned. I'd like to get it into main. This is just a squashed and rebased version of that PR, with one change:

• Current ArgoCD merge behavior works like InnerJoinUnique, but the original PR set the default to LeftJoinUnique. I've changed the default to InnerJoinUnique for backwards compatibility.

(TBH i'm not sure what the use case is for the non-unique merge strategies. I have no objection to removing the non-unique strategies if it helps get this PR approved.)

Also, I'm having a rough time running the toolchain even after following the guide, therefore codegen has not been run. I'm hoping a maintainer can help me kick this across the finish line 🙏🏻

Fixes #11952, #12837, #14560

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Toolchain Guide
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

[bunnyshell]

✅ Preview Environment deployed on Bunnyshell

Component	Endpoints
argocd	https://argocd-jicrwi.bunnyenv.com/
argocd-ttyd	https://argocd-web-cli-jicrwi.bunnyenv.com/

See: Environment Details | Pipeline Logs

Available commands (reply to this comment):

• 🔴 /bns:stop to stop the environment
• 🚀 /bns:deploy to redeploy the environment
• ❌ /bns:delete to remove the environment

[joshfrench]

having a rough time running the toolchain

specifically, make codegen is failing with the following and neither make build nor make test will run, presumably as a result.

+ go-to-protobuf --go-header-file=/go/src/github.com/argoproj/argo-cd/hack/custom-boilerplate.go.txt --packages=github.com/argoproj/argo-cd/v2/pkg/apis/application/v1alpha1 --apimachinery-packages=+k8s.io/apimachinery/pkg/util/intstr,+k8s.io/apimachinery/pkg/api/resource,+k8s.io/apimachinery/pkg/runtime/schema,+k8s.io/apimachinery/pkg/runtime,k8s.io/apimachinery/pkg/apis/meta/v1,k8s.io/api/core/v1,k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1 --proto-import=/go/src/github.com/argoproj/argo-cd/vendor --proto-import=/dist/protoc-include --output-dir=/go/src/
2025/01/09 21:27:30 protoc -I . -I /go/src/ -I /go/src/github.com/argoproj/argo-cd/vendor -I /dist/protoc-include --gogo_out=/go/src/ /go/src/k8s.io/api/core/v1/generated.proto
2025/01/09 21:27:30 Could not make proto path relative: /go/src/k8s.io/api/core/v1/generated.proto: No such file or directory