feat(search-index): add search-index export and import commands

[rs-amp]

This PR adds search index export and import commands.

The export command is rather straightforward - it scans all search indexes in the hub, enriches them with related info such as its settings, assigned content types, keys and replicas, and dumps them to a JSON file for each index. Replicas do not appear as individual files - they are contained within their parent search index's file.

Webhooks are also exported with each search index, into the webhooks/ subfolder of the target directory. These include their webhook id, which is referenced by the fields of EnrichedAssignedContentType so that the webhook can be found from these files when importing.

On import, search indexes are created or updated depending on if a match with the same name is found, and if its content does not match the search index being imported. Settings are synchronised afterwards, including a list of all replicas. The import uses a union of both the existing replicas and the replicas in the import file to determine what replicas to put in the settings, and update the settings of. Replicas are never deleted - as their names are unique and reserved, deleting them would cause issues.

Assigned content types are created automatically, and will try to sync with what you are importing - including deleting assignments that are not present on the file being imported. By default, each assigned content type uses the default webhooks created when the type was created - or the existing webhooks if the assignment already existed.

Optionally, the user can provide a --webhooks flag, which allows importing webhooks relating to assigned content types within search indexes. When importing webhooks, the command attempts to rewrite occurrences of the withDeliveryContentItem tag within the webhook body to point to the target hub's name and virtual staging environment. If different, this new body and any other related properties are copied to the target webhook.

A clone step is also added for search indexes, which occurs immediately before content item import, so that step triggers any webhooks. Similar to extensions, the revert version of this step does not delete search indexes, as the names are unique and reserved on creation. Deleting them might make them impossible to recreate in the future, so we prefer to leave them alive to update in the future instead.

[rs-amp]

Depends on amplience/dc-management-sdk-js#95. After that's merged, package.json must be updated.