Add `--target-api-url` to `gh gei` commands

[ArinGhazarian]

Right now for GHAE migrations, gh gei supports passing the --target-api-url to migrate-repo command to be able to make API calls against non default (https://api.github.com) bases addresses. The problem is that no other command in gh gei supports passing the --target-api-url in. We need to add the arg to all other gh gei commands and also make necessary changes to the generate-script command.

Todo

• [x] Add --target-api-url to all gh gei commands.
• [x] Modify generate-script to support passing the --target-api-url to gh gei commands.

[dylan-smith]

This should also be added to ado2gh

[dylan-smith]

Since we're no longer planning to support migrations TO GHAE I'm closing this issue.