tiproxy: add note about reloading certificates once an hour (#22138)

[ti-chi-bot]

This is an automated cherry-pick of #22138

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• https://github.com/pingcap/tiproxy/blob/d9ef65aa16552e7b76ed51d6bf5ce7c0a1504ecd/pkg/manager/cert/manager.go#L96-L121
• https://github.com/pingcap/tiproxy/blob/d9ef65aa16552e7b76ed51d6bf5ce7c0a1504ecd/pkg/manager/cert/manager.go#L21

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[gemini-code-assist]

Summary of Changes

Hello @ti-chi-bot, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request updates the TiDB documentation to provide crucial information about how TiProxy manages TLS certificates. It specifically highlights that TiProxy reloads certificates from disk on an hourly basis, which means any modifications to certificate files will have a delay of up to one hour before they become active. This clarification aims to improve user understanding of certificate management within TiProxy.

Highlights

• Documentation Update: Added important information to the TiDB documentation regarding TiProxy's certificate reloading mechanism.
• Certificate Reload Frequency: Clarified that TiProxy reloads certificates from disk once every hour.
• Impact of Certificate Changes: Noted that any changes made to certificate files on disk might take up to one hour to take effect due to the hourly reload cycle.

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[gemini-code-assist]

Code Review

This pull request adds a note to the documentation regarding TiProxy's hourly certificate reloading. The change is reflected in two files. My review includes a critical comment to resolve merge conflict markers found in enable-tls-between-components.md. I've also provided a suggestion for tiproxy/tiproxy-configuration.md to make the new note more concise, in line with the repository's style guide which advises against unnecessary words.

[gemini-code-assist]

This file contains merge conflict markers (<<<<<<<, =======, >>>>>>>). Please resolve these conflicts to ensure the document renders correctly.

Suggested change

	<<<<<<< HEAD
	=======
	- TiProxy reloads certificates from disk once an hour.
	>>>>>>> 9cff933fa3 (tiproxy: add note about reloading certificates once an hour (#22138))
	- TiProxy reloads certificates from disk once an hour.

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Test name	Commit	Details	Required	Rerun command
pull-verify	4b99b89	link	true	/test pull-verify

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