encryption-at-rest: Update (#6152)

[ti-chi-bot]

This is an automated cherry-pick of #6152

What is changed, added or deleted? (Required)

Updating "Encryption at Rest" docs:

• Add note about using AWS KMS for on-premise deployment
• Add notes about key creation (e.g. to use the right key type)
• Fix the syntax of the encryption section configuration
• Add note about VPC endpoints for KMS
• Add note about multi-Region keys
• Add information about data-at-rest support in PD ( Support Transparent Data Encryption(TDE) for PD tidb#18262 )
• Remove some of the references to pre-v5.0 versions ( encryption-at-rest: Update #6152 (comment) )
• Use 168h instead of 7d as PD doesn't support d as unit specifier. ( data-key-rotation-period doesn't accept duration in days. tikv/pd#3987 )
• Added a note about EBS Encryption

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

• master (the latest development version)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)
• v4.0 (TiDB 4.0 versions)
• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• TomShawn

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[TomShawn]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 3d02bcf