feat: frogbot support for yarn workspaces

[sean-perkins]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• This pull request is on the dev branch.
• I used gofmt for formatting the code before submitting the pull request.
• Update documentation about new features / new supported technologies

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Relates to #798

Frogbot fails to apply dependency fixes in Yarn workspace (monorepo) projects. When a vulnerability is detected in a workspace package the fix command is run from the workspace package's subdirectory, but yarn upgrade/yarn up must be run from the workspace root against a specific workspace. This PR adds workspace detection.

A secondary bug is also fixed: isYarnV1Project previously ran the global yarn --version binary to determine the project's Yarn version. Projects using Yarn Berry ship their own binary via .yarnrc.yml yarnPath, so the global version could be wrong. The new implementation reads the version directly from the yarnPath filename in .yarnrc.yml, which is faster and version-agnostic.