Extend the D1 how much worker can a database can do

[lambrospetrou]

Summary

Rewording the D1 documentation about how much work can be done since this is a very common question by D1 users.

Screenshots (optional)

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[vy-ton]

• should mention how replication alters this
• could raise reader question of durability

[lambrospetrou]

This doesn't really change though if we take each replica separately.

I can add a sub-section at the end for read replication to add some clarification.

[lambrospetrou]

Suggested change

	Each individual D1 database is backed by a single [Durable Object](/durable-objects/concepts/what-are-durable-objects/).
	Each individual D1 database is backed by a single [Durable Object](/durable-objects/concepts/what-are-durable-objects/). When using [D1 read replication](https://developers.cloudflare.com/d1/best-practices/read-replication/#primary-database-instance-vs-read-replicas) each replica instance is a different Durable Object and the guidelines apply to each replica instance independently.

@vy-ton what do you think?