Define Read and Write Elasticsearch index names to leverage alias

An alias can point to multiple indexes on search operation.
But write operation requires a single index.
So we need 2 index names.

By using 2 alias names we can manage complex cases, like:

• Reindex repository without downtime:
  • On reindexing create a new index and point write alias to it
  • When completed point the search alias to the new index
  • The old index can be dropped

Note that searches that occur during reindexing will not match documents modified or created during reindexing, this is still better as seeing only the reindexed one.

• Archived or limited Audit:
  By pointing the write index alias to a new index every month and defining a search alias over the 12 last index we limit the audit to the last year.
  Note that this administration task can be done outside of Nuxeo, it is just manipulating alias definition here.

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New parameters have been added to the index descriptor:

• manageAlias=true: Nuxeo will manages 2 aliases: one for searching using the name of the contrib (default to "nuxeo"), one for writing with a "-write" suffix ("nuxeo-write"), both aliases will point to the same index ("nuxeo-0000"). When reindexing the repository a new index is created ("nuxeo-0001") and the write alias is updated to use it, the search alias stay on the previous index ("nuxeo-0000"). Once indexing is termintated the search alias is updated to point to the new index (nuxeo-0001). It is up to the adminitrator to clean old non used index (keep the 2 last created for instance)
• writeAlias: When specified the write is done on this alias, nuxeo will not manage any aliases. The use case is for managing time based index for audit, one can create a new index every month the search alias can point to multiple indexes.