minor #18878 [Doctrine] Update the article about Doctrine events (javiereguiluz)

This PR was squashed before being merged into the 6.3 branch.

Discussion
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[Doctrine] Update the article about Doctrine events

Fixes #18650 and #18181.

Changes in this PR:

* Reworded the introduction to only explain the 3 types of listeners which are not deprecated and better explain why/when to use them according to #18650
* Reordered the explanation of the listeners to match the same order as in the intro: `Lifecycle callbacks` -> `Entity listeners` -> `Lifecycle listeners`
* Removed the contents about "Lifecycle Subscribers" because they are deprecated

Commits
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4a4d9de [Doctrine] Update the article about Doctrine events

Author: javiereguiluz