[FEATURE] Support timestamp fields in workflows

[ohltyler]

A common field for plugin resources include timestamps indicating when a resource is created / updated / deployed. This is also a requirement based on the latest @opensearch-project/opensearch-ux mocks for the frontend (refer to mock in opensearch-project/dashboards-flow-framework#65). I propose the following added fields:

• last_update_time in the workflows system index, and updating using the current timestamp when a POST/PUT request is made.
• last_launched_time (no strong opinion on the name) in the workflows state index indicating when a provision/launch was last executed. This could be updated the same time the provisioning progress field is updated, for example.

[ohltyler]

Update: from searching through the codebase, I do see a LAST_UPDATED_TIME_FIELD, but I don't see it being used/indexed in the workflows system indices anywhere, and it is not included in any search API responses as a result.