SEAB-6000: Propagate both the "added" and "removed" varieties of the "installation_repositories" event

[svonworl]

Description
This PR changes the upsertGitHub lambda to propagate both possible varieties of the "installation_repositories" event (wherein the action is either "added" or "removed") to the webservice.

Regarding the code style, it's not how I would have formatted/indented the code, but that's what our tests require.

Had remove the duplicate <repository> lines from that pom to make the tests pass.

After this PR merges, I will update dockstore-deploy to incorporate the corresponding commit.

Review Instructions
https://ucsc-cgl.atlassian.net/browse/SEAB-6000

Testing
See dockstore/dockstore#5852

Security
No concerns.

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[coverbeck]

Will this require downtime when we install this version? I think so, we don't want 1.15 getting any of these events do we? And we don't want 1.16 getting any of the 1.15 formatted events?

If downtime is required, can you please update the 1.16 deploy notes.

[svonworl]

Will this require downtime when we install this version? I think so, we don't want 1.15 getting any of these events do we? And we don't want 1.16 getting any of the 1.15 formatted events?

If downtime is required, can you please update the 1.16 deploy notes.

The previous lambda propagates installation_repositories events that contain an "added" action, this new lambda propagates all versions of the event. An event with an "added" action contains the affected repositories in the repositories_added field, which the old webservice inspects to figure out which repos got added. An event with a "removed" action should have an empty repositories_added field, so if such an event reaches the old webservice, I believe it's a no-op, so no downtime required.