feat: support new Dgraph connection string format

[mattjohnsonpint]

Description

• Update to latest DGo client and refactor
• Support the new connection string format (specified as "connString" in the manifest, similar to other DBs)
• Misc cleanup

Checklist

All PRs should check the following boxes:

• I have given this PR a title using the
  Conventional Commits syntax, leading with fix:,
  feat:, chore:, ci:, etc.
  • The title should also be used for the commit message when the PR is squashed and merged.
• I have formatted and linted my code with Trunk, per the instructions in
  the contributing guide.

If the PR includes a code change, then also check the following boxes. (If not, then delete the
next section.)

• I have added an entry to the CHANGELOG.md file.
  • Add to the "UNRELEASED" section at the top of the file, creating one if it doesn't yet exist.
  • Be sure to include the link to this PR, and please sort the section numerically by PR number.
• I have manually tested the new or modified code, and it appears to behave correctly.
• I have added or updated unit tests where appropriate, if applicable.

[linear]

HYP-3159 Support new Dgraph connection string syntax in Modus

[Copilot]

Pull Request Overview

This PR updates the Dgraph client integration to support a new connection string format by refactoring how connections are created and managed. Key changes include:

• Replacing the legacy gRPC connection approach with connection string and grpc target based methods.
• Removing the old auth credentials handling and associated imports.
• Updating the manifest structure and tests to support the new connection string field.

Reviewed Changes

Copilot reviewed 7 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
runtime/dgraphclient/registry.go	Refactored connection creation and shutdown logic; added new branches for connection string handling.
runtime/dgraphclient/dgraph.go	Removed grpc.ClientConn field and introduced a constructor for the new connector.
lib/manifest/test/manifest_test.go	Added tests for the new connection string usage in Dgraph connections.
lib/manifest/dgraph.go	Updated DgraphConnectionInfo to include the new connString field.
CHANGELOG.md	Changelog updated to include the new Dgraph connection string feature.

Files not reviewed (4)

• lib/manifest/modus_schema.json: Language not supported
• lib/manifest/test/valid_modus.json: Language not supported
• runtime/go.mod: Language not supported
• sdk/go/go.mod: Language not supported

Comments suppressed due to low confidence (2)

runtime/dgraphclient/registry.go:42

• Verify that the new dgraph client's Close() method properly releases all underlying resources, as it replaces the previous grpc.ClientConn.Close().

connector.dgClient.Close()

runtime/dgraphclient/registry.go:74

• [nitpick] Consider rephrasing the error message for when both connString and grpcTarget (or key) are provided to give clearer guidance on which option to use.

if connection.GrpcTarget != "" {