Add Dynamic Type

[SpencerTorres]

PR text is pending update

Note: There are some server-side bugs that need to be fixed/merged, including a protocol update. However, this PR can still be reviewed as-is.

Summary

Implement Dynamic column type. Partially resolves #1430.

Usage

As for usage, this is the same as Variant and VariantWithType, except the types are named as Dynamic and DynamicWithType. These are Go type aliases and are effectively the same type from the user side. See Variant PR for details (#1453).

Since Dynamic type starts as a blank Variant, it is best to append using DynamicWithType so the underlying column can be created correctly. If a type isn't specified, a type inference function is used, but this may not always work as intended.

Examples are included in examples folder.

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials