[.NET] Update sample connectors' metadata

[timtay-microsoft]

Also remove some unused fields from the sample kubernetes resources

The TCP sample had an outdated metadata doc and the TCP + SQL connectors had no metadata doc.

These metadata docs won't actually be published since these connectors aren't published. However, they are here as a reference to those who write connectors.

Also add a check in the gates for validating that these samples' metadata matches the connector metadata schema

[Copilot]

Pull request overview

Updates the .NET sample connectors to use the newer AIO connector metadata schema and simplifies some sample Kubernetes asset resources by removing unused fields.

Changes:

• Added connector-metadata.json files for the SQL and REST polling sample connectors using the aio-connector-metadata-10.0-preview schema.
• Updated the Event Driven TCP connector’s metadata file to the new schema format.
• Removed unused dataSource fields from sample asset definition YAMLs.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
dotnet/samples/Connectors/SqlConnector/connector-metadata.json	Adds new connector metadata for the SQL sample connector.
dotnet/samples/Connectors/SqlConnector/KubernetesResources/sql-server-asset-definition.yaml	Removes an unused/invalid dataSource field from the asset definition.
dotnet/samples/Connectors/PollingRestThermostatConnector/connector-metadata.json	Adds new connector metadata for the REST polling thermostat connector.
dotnet/samples/Connectors/PollingRestThermostatConnector/KubernetesResources/rest-server-asset1-definition.yaml	Removes an unused/invalid dataSource field from the asset definition.
dotnet/samples/Connectors/EventDrivenTcpThermostatConnector/connector-metadata.json	Updates metadata format, but currently does not match the TCP connector sample and appears structurally invalid.