refactor(gce): Refactor BasicGoogleDeployHandler to be more readable and testable

[edgarulg]

Key point about the refactor.

1. I translated the whole class BasicGoogleDeployHandler into java.
2. I split up the handle method into small single responsibility methods.
3. I defined unit testing for most of the new methods I created to prove functionality.
4. I do not include any new feature or change that was not defined by the BasicGoogleDeployHandler before.

Related to: spinnaker/spinnaker#6985

[edgarulg]

I published and deployed a snapshot version with my refactor and I validated a GCE deploy worked as expected. I didn't tests all possible configurations as part of my e2e validation.

[edgarulg]

@Mergifyio refresh

[mergify]

refresh

✅ Pull request refreshed

[edgarulg]

@Mergifyio rebase

[mergify]

rebase

☑️ Nothing to do

• -conflict [📌 rebase requirement]
• -closed [📌 rebase requirement]
• queue-position = -1 [📌 rebase requirement]
• any of:
  • #commits > 1 [📌 rebase requirement]
  • #commits-behind > 0 [📌 rebase requirement]
  • -linear-history [📌 rebase requirement]