feat: Notify the user when an error is encountered when adding new accounts (#1252)

[Cubik65536]

Description

• Replace GitURL.baseURL with SourceControlAccount.Provider.apiURL and GitURL.webURL with SourceControlAccount.Provider.baseURL to prevent confusion between usage of these URLs.
• Place the duplicate account check before signing request process
  • This can reduce the amount of useless API requests as, in this case, no matter the request result, the account can't be added anyway.
• Alert the user when trying to add an existing account.
• Alert the user when there's no internet connection.
• Alert the user when signin request failed.
  • GitHub
  • GitLab

Related Issues

• closes ✨ Notify the user when an error is encountered when adding new accounts #1252

Checklist

• I read and understood the contributing guide as well as the code of conduct
• The issues this PR addresses are related to each other
• My changes generate no new warnings
• My code builds and runs on my machine
• My changes are all related to the related issue above
• I documented my code

Screenshots

Video Demo:

2023-05-01.00-22-11.mov

[austincondiff]

It looks like there is a SwiftLint error. Please resolve.

[Cubik65536]

It looks like there is a SwiftLint error. Please resolve.

fixed

[austincondiff]

Looks great!