Fix Vale issues for planned_failover_single_node.md

What does this MR do?

This MR addresses the changes requested by Vale to convert the documentation of the ( ./planned_failover_single_node.md ) file, from future tense to their relative tense other than future tense.
So all the future tense words and phrases have been replaced with equivalent tense phrases other than future tense so that Vale gives no errors during checking.

Related issues

Fix-Vale-issues-for-planned_failover_single_node.md #332113 (closed)

Author's checklist (required)

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For suggestions that you are confident don't need to be reviewed, change them locally and push a commit directly to save others from unneeded reviews. For example:

• Clear typos, like this is a typpo.
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