Indexing pause framework

Background

I believe that we need to start designing indexing pause framework to allow us to selectively pause indexing operations.

Proposal

We can start with something like:

• document_type (blobs, issues)
• alias_name/index_name

This framework needs to be extendable so that we can eventually reach project_id granularity. The first use-case for this framework can be Zero downtime reindexing should pause only the ... (#381705)

I think it should be a postgresql table. We can call it advanced_search_pause_rules

name	type	comment
id	bigint	PRIMARY KEY
rule	jsonb	NOT NULL
created_at	timestamp	NOT NULL
updated_at	timestamp	NOT NULL

We then can cache all the rules based on MAX(updated_at) so that we don't need to read the table every time.