enable-tls-for-mysql-client: add tiproxy

[dveeden]

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Related: pingcap/tidb-operator#5825

[ideascf]

We do mTLS between components of a TC so that this cert is presented as both server-side cert and client-side cert.

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[Oreoxmt]

I've updated the base branch for this PR from master to release-1.x, as release-1.x is now the active development branch for TiDB Operator v1.x documentation.