Replace node number with node count

[yahonda]

What is changed, added or deleted? (Required)

The current "node number" refers to the specific identification or label given to each instance. "node count" should refers to the quantity or count of instances, that is needed here. I think "the number of TiDB/TiFlash nodes" are fine.

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s): *: Replace Instance Number with Number of Instances #14639 there was a similar pull request that replaces the instance number with number of nodes. In this pull request, I use the count to make differences smaller.

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

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[hfxsd]

Suggested change

	#### Estimate TiKV node nucountmber according to data volume
	#### Estimate TiKV node count according to data volume

[hfxsd]

PRs for TiDB Cloud should be created based on the v8.1 branch instead of master. Can you change it to the v8.1 branch? Thanks.

[yahonda]

PRs for TiDB Cloud should be created based on the v8.1 branch instead of master. Can you change it to the v8.1 branch? Thanks.

Just changing the base branch release-8.1 makes a lot of unrelated commits. I will create another pull request.

[yahonda]

Just changing the base branch release-8.1 makes a lot of unrelated commits. I will create another pull request.

Opened #20811 for the release-8.1 branch.