[documentation] "The flat ledger manager is the default" is a false claim

[lhotari]

The documentation claims that "The flat ledger manager is the default".
https://github.com/apache/bookkeeper/blob/master/site/docs/latest/getting-started/concepts.md#use-the-flat-ledger-manager-in-most-cases

However, the default is HierarchicalLedgerManagerFactory and this can be seen at

bookkeeper/bookkeeper-server/src/main/java/org/apache/bookkeeper/meta/AbstractZkLedgerManagerFactory.java

Line 316 in a0d49fc

factoryClass = HierarchicalLedgerManagerFactory.class;

The documentation for configuration already mentions hierarchical as the default

bookkeeper/site/_data/config/bk_server.yaml

Lines 485 to 495 in 94912a9

	- name: Metadata Service Settings
	params:
	- param: metadataServiceUri
	description: metadata service uri that bookkeeper is used for loading corresponding metadata driver and resolving its metadata service location.
	default: "zk+hierarchical://localhost:2181/ledgers"
	- param: ledgerManagerFactoryClass
	description: |
	@Deprecated in favor of using `metadataServiceUri`
	The ledger manager factory class, which defines how ledgers are stored, managed, and garbage collected. See the [Ledger Manager](../../getting-started/concepts#ledger-manager) guide for more details.
	default: hierarchical

However, It would be better to remove "The flat ledger manager is the default " from the sentence in concepts.md.

[eolivelli]

You are right
It is also deprecated.

Can you please send PR? The website is in this repository

[lifepuzzlefun]

submit a pr here #2413