Update WAL failover docs with additional feedback

[rmloveland]

Fixes DOC-11733

Deploy preview:

• WAL failover

[github-actions]

Files changed:

• src/current/images/v24.3/wal-failover-behavior.png:
• src/current/v24.3/wal-failover.md
• src/current/images/v24.3/wal-failover-overview.png:
• src/current/v24.3/wal-failover.md
• src/current/v24.3/wal-failover.md

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[rmloveland]

@dshjoshi this PR adds the slides from the enablement deck that you messaged me about adding

we can also make other updates to the doc here as well if you want

[rmloveland]

@jbowens removed you since there are no substantive changes in this PR, just adding some slides as requested by @dshjoshi

@dshjoshi please take a look and let me know what you think! I've added some images from your enablement slides as requested - here is the preview: WAL failover

[rmloveland]

@dshjoshi ping on this - mind taking a look?