feat: Merge local bunfig with action scope/registry config

[vitoorgomes]

Auth is now able to merge local config with the necessary scope + registry url without duplicating or doing some weird things when a local config already exists.

It covers:

• No local bunfig.toml
• When local bunfig.toml does not have any [install.scopes]
• When local bunfig.toml does have a [install.scopes] and it's not the same as the action
• When local bunfig.toml does have a [install.scopes] and it's the same as the action

It will be able to merge all without conflicting keys

#33

I also created some tests and added to the github actions as a new step

[xhyrom]

Thanks you for this!