Adds documentation for the Delta Lake Read Managed I/O

[chamikaramj]

Also, raises exceptions for currently unsupported reading of a specific version/timestamp.

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R: @ahmedabu98 for label java.
R: @Abacn for label website.

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[Abacn]

Thanks. Checked GCS Staging website. A few findings

• managed-io.md entry is hard to find. Consider adding a link in https://apache-beam-website-pull-requests.storage.googleapis.com/39495/documentation/io/connectors/index.html ?

e.g. the first graph states

I/O connectors denoted as Supported via Managed API can be accessed using the simplified managed I/O APIs for Java and Python.

We can add a link for [managed I/O APIs] to io/managed-io.md‎.

Consider add DeltaLakeIO to the Built-in I/O Connectors list