Release version 0.2.0

[sd2k]

Bump the crate to v0.2.0.

Changes:

Added

• Bump arrow2 dependency to 0.10.0, and re-export it as grafana_plugin_sdk::arrow2
• Added new data field to SubscribeStreamRequest and SubscribeStreamResponse,
  matching the latest release of the protobuf descriptors.
• More types now impl FieldType and IntoFieldType, meaning that iterators or vecs of them can be turned into Fields:
  • bool
  • SystemTime
  • chrono::Date
  • chrono::NaiveDate
  • chrono::NaiveDateTime
• The FieldType and IntoFieldType traits are now public. These are useful when
  writing generic functions to convert iterators, vecs, slices or arrays into Fields.

Changed

• Mark the various Request and Response structs in the backend part of the SDK as
  #[non_exhaustive] since changes to those structs are largely outside of our control;
  the protobuf descriptors may add additional fields, and this allows us to include them
  without breaking our API. Some Response types now have new constructors which should
  be used.
• Most of the exported types in the data part of the SDK are also now non-exhaustive,
  for the same reason as above. These types now either have separate constructors or
  Default impls which can be used to create them.
• Derive Clone for various backend structs:
  • AppInstanceSettings
  • DataSourceInstanceSettings
  • PluginContext
  • Role (is also now Copy)
  • TimeRange
  • User
• Change the Iter associated type of backend::DataService to Stream, and update
  the return type of query_data accordingly. This allows each inner query to be handled
  asynchronously and concurrently in a simple way.
• The live::Error type is now an enum and provides more detail on failures.
• The path field of SubscribeStreamRequest, RunStreamRequest and
  PublishStreamRequest are now live::Path types rather than arbitrary strings.