Create standard steps for creating database dumps

Problem/Motivation

This is a follow-up to #3264120: Remove aggregator module and our dependency on Laminas Feed to discuss documentation updates regarding database dumps. I am copying comment #42, by catch, from that issue to here.

To fix (hopefully) the dumps, this is what I did:

gunzip core/modules/system/tests/fixtures/update/drupal-9.3.0.filled.standard.php.gz

Edited it and manually added the if statements from #3261629: Database dumps are no longer driver-agnostic (top and bottom of the file).

gzip core/modules/system/tests/fixtures/update/drupal-9.3.0.filled.standard.php

We should try to find a way to have standard steps to generate the dumps that don't reintroduce this issue though - it might been copying the dump scripts from 9.4.x or 10.0.x out of the git tree before switching to 9.3.0, or loading the database into 9.3.0, making changes, then switching to 9.4.x (or 9.3.whatever) before running the dump script. Or a time machine to apply the commit to 9.3.0

From catch these two issues have relevant notes about making dumps. #3275093: Drupal 9.3.0 dumps were created with PHP 8, needs to be PHP 7.3 and #3290810: Remove updates added prior to 9.4.0 (9.4.4 for ckeditor) and add 9.4.0 database dumps.

Steps to reproduce

Proposed resolution

Move the section, Creating your own dump to a new page and expand the instructions.

Remaining tasks

Decide on the text of the new instructions

User interface changes

API changes

Data model changes

Release notes snippet