Add support for GCP + Oauth2 credentials

[uz1pk]

Before this PR

• Support GCP oauth creds external-systems#16
• Add oauth credentials type to source credentials api external-systems#17

After this PR

• Bump external-systems
• Add support for GCP + Oauth2 creds generated by backend

Are Docs needed?

• README.md already links to external-systems lib which references this

[changelog-app]

Generate changelog in changelog/@unreleased

Type (Select exactly one)

• Feature (Adding new functionality)
• Improvement (Improving existing functionality)
• Fix (Fixing an issue with existing functionality)
• Break (Creating a new major version by breaking public APIs)
• Deprecation (Removing functionality in a non-breaking way)
• Migration (Automatically moving data/functionality to a new system)

Description

Bump external-systems lib

Check the box to generate changelog(s)

• Generate changelog entry

[changelog-app]

✅ Successfully generated changelog entry!

What happened?

Your changelog entries have been stored in the database as part of our migration to ChangelogV3.

Need to regenerate?

Simply interact with the changelog bot comment again to regenerate these entries.

[Copilot]

Pull Request Overview

This PR adds support for GCP OAuth2 and generic OAuth2 credentials by bumping the external-systems dependency and implementing credential parsing for these new authentication types.

• Bumps external-systems from ^0.100.0 to ^0.107.0 to support new credential types
• Adds parsing logic for GCP OAuth2 and generic OAuth2 credentials in the source configuration
• Expands test coverage to verify the new credential types work correctly

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
pyproject.toml	Updates external-systems dependency version to support new credential types
compute_modules/sources_v2/_sources.py	Adds credential parsing functions for GCP OAuth2 and generic OAuth2 credentials
tests/sources_v2/test_sources.py	Adds comprehensive test coverage for the new credential types and refactors existing test names

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.
You can also share your feedback on Copilot code review for a chance to win a $100 gift card. Take the survey.}

[autorelease3]

Released 0.28.0