Enable multi_ack and multi_ack_detailed capabilities

[pjbgf]

Enabling multi_ack and multi_ack_detailed allows the use of go-git against Azure DevOps.
Those capabilities are not fully implemented, however they have no impact for "fresh new fetches", which are the primary use case for Flux.

⚠️ Using this version to deal with existing repositories or to call additional fetch/pull operations against Azure DevOps will result in:

empty git-upload-pack given

This change was tested against a range of Git Service Providers to ensure no regression was being introduced.
Note that the tests were completed on the scope of Source and Image Automation Controllers, which only use a subset of the Git features implemented by go-git.

https-aws-codecommit
https-bitbucket
https-devops-flux-testing
https-gitlab
https-google-code
ssh-ecdsa-bitbucket
ssh-ecdsa-gitlab
ssh-ecdsa-google
ssh-ed25519-bitbucket
ssh-ed25519-gitlab
ssh-ed25519-google
ssh-rsa-aws-codecommit
ssh-rsa-bitbucket
ssh-rsa-devops
ssh-rsa-gitlab
ssh-rsa-google

The blue line in the graph below represents rate(go_memstats_alloc_bytes_total{app="source-controller"}[$__rate_interval]) and shows a stable memory profile throughout the 6h. The same has been observed since the beginning of the tests (+19h).

For the purposes of the tests, all the repositories had their spec.gitImplementation set to go-git, the controller has its libgit2 managed transport disabled and OptimizedGitClones=false. The controller was set to have 40 workers to quickly iterate through the 35 GitRepository objects. Most target sources have at least one large file (~100mb). The reconciliation intervals are set to 30s, forcing the reconciliations to be overlapping every so often.

Additional memory and GC related settings:

      - op: replace
        path: /spec/template/spec/containers/0/resources/limits/memory
        value: 1200Mi
      - op: replace
        path: /spec/template/spec/containers/0/resources/requests/memory
        value: 1200Mi
      - op: add
        path: /spec/template/spec/containers/0/env/0
        value:
          name: GOMEMLIMIT
          value: "800MiB"
     - op: add
        path: /spec/template/spec/containers/0/env/0
        value:
          name: GOGC
          value: "100"

For completeness, an additional graph without go_memstats_alloc_bytes_total so it is easier to track GC duration and goroutine numbers:

[aryan9600]

lgtm! 🚀
we should probably change the PR title to something like Enable multiack capability?

[mestadler]

Can we look at Gitea as well?