Write push result output variables

[APErebus]

Updates output variables to correctly track commited changes for each application and source.

We're tracking:

• Commit SHA
• Short SHA
• PR title
• PR url
• PR number

These values will be used for subsequent operations, such as:

• Waiting for the raised PR to be merged
• Determining which commit Octopus has made it's changes on

Example result for a direct commit

[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-image-tags-yaml-octopub-test].Source[0].CommitSha] = '2e4e752201502099ce74ab3641dc70a4d255f723' 
[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-image-tags-yaml-octopub-test].Source[0].ShortSha] = '2e4e752201'

Multi-source direct commit

[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-manifests-yaml-multisource-test].Source[0].CommitSha] = '6ddf850cb9a29b22703a911185935fe3d683c7d7' 
[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-manifests-yaml-multisource-test].Source[0].ShortSha] = '6ddf850cb9' 
[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-manifests-yaml-multisource-test].Source[1].CommitSha] = '323c6344a7001d911254f3e43e80299dadd2d3bc' 
[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-manifests-yaml-multisource-test].Source[1].ShortSha] = '323c6344a7' 

Pull request

[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-image-tags-yaml-octopub-test].Source[0].CommitSha] = '4e61beba829ba9dc2a13075f0e0494a02ed43401' 
[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-image-tags-yaml-octopub-test].Source[0].PullRequest.Number] = '1' 
[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-image-tags-yaml-octopub-test].Source[0].PullRequest.Title] = 'Octopus Deploy updated image versions' 
[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-image-tags-yaml-octopub-test].Source[0].PullRequest.Url] = 'https://github.com/xxx/yyy/pull/1' 
[Octopus.Action[Update Image Tags].Output.ArgoCD.Gateway[terraform-argo-gateway].Application[update-image-tags-yaml-octopub-test].Source[0].ShortSha] = '4e61beba82' 

Note: There is currently a known issue where multiple ArgoCD applications with the exact same source and using the direct commit method will not have this data reported. This is not addressed in this PR.

(PR taken over by @eddymoulton)

Closes MD-1514

[eddymoulton]

Approach seems fine to me 🤷

[APErebus]

LGTM!

[flin-8]

nit: It would be clearer if we just short circuited and returned the push result here

[flin-8]

LGTM