tiproxy: add note about reloading certificates once an hour

[qiancai]

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What is changed, added or deleted? (Required)

References:

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

• This PR is translated from: tiproxy: add note about reloading certificates once an hour docs#22138
• Other reference link(s):

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• Delete files
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• Might cause conflicts after applied to another branch

[Oreoxmt]

Rest LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-12-09 06:50:30.517669063 +0000 UTC m=+937375.331446625: ☑️ agreed by Oreoxmt.

[ti-chi-bot]

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