Add Extract/Publish mechanism from APIOps to this extension

[ross-p-smith]

This PR is open for comment about the direction to take for adding APIOps capability to this extension.

• I have left the old 'extract ARM' functionality there although I believe it should be removed as it depends on .Net 2.1 and the DevOps Toolkit itself is deprecated.
• I have added a DevContainer for ease of development
• I download the 2 binaries required for import/export when the Extension is first activated as this reduces the size by 140Mb.

Things yet to do

• Feature flag hide the old functionality

Relates to #324

[ross-p-smith]

When you first invoke the extension, it will download binaries in the background

[ross-p-smith]

Two new menu items (APIOps) to extract and publish

Extract Service is the older DevOps Toolkit version that requires .Net 2.1 installed to work.

[quanterion]

LGTM. Just general remark is looks like APIOps support exporting just spec (like OpenApi for REST) and we need to add new APIs like OData there

[ross-p-smith]

Currently ApiOps only supports specifications, not OData endpoints - I have raised the following issue to track this: - Azure/apiops#419