Fix broken external links (#22901)

[ti-chi-bot]

This is an automated cherry-pick of #22901

What is changed, added or deleted? (Required)

Fix broken external links reported in #22897:

• Update the TiDB Operator EBS snapshot restore link.
• Replace stale Dify, Zapier, and Flashduty documentation links with current destinations.
• Remove references to external pages that no longer have stable reachable targets.

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

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 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)

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

• This PR is translated from:
• Other reference link(s): Fixes Broken Link Detected #22897

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

[ti-chi-bot]

@qiancai This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

@ti-chi-bot: ## If you want to know how to resolve it, please read the guide in TiDB Dev Guide.

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[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-verify	2dfc33e	link	true	/test pull-verify

Full PR test history. Your PR dashboard.

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[gemini-code-assist]

Code Review

This pull request updates several external links and removes redundant documentation across multiple files, including updates for Dify, Zapier, and EBS volume snapshots. A critical issue was identified in tidb-cloud/monitor-alert-flashduty.md, where Git merge conflict markers were accidentally committed. A suggestion has been provided to resolve this conflict and restore the correct link format.

[gemini-code-assist]

It appears that Git merge conflict markers (<<<<<<<, =======, >>>>>>>) were accidentally committed to this file. Please resolve the conflict by removing the markers and keeping the updated link.

Suggested change

	<<<<<<< HEAD
	1. Generate a webhook URL by following the instructions in [Flashduty Prometheus Integration](https://docs.flashcat.cloud/en/on-call/integration/alert-integration/alert-sources/prometheus#prometheus-integration-guide).
	=======
	1. Generate a webhook URL by following the instructions in [Flashduty Prometheus Integration](https://docs.flashcat.cloud/en/on-call/integration/alert-integration/alert-sources/prometheus).
	>>>>>>> 6993fea054 (Fix broken external links (#22901))
	1. Generate a webhook URL by following the instructions in [Flashduty Prometheus Integration](https://docs.flashcat.cloud/en/on-call/integration/alert-integration/alert-sources/prometheus).