[Task]: Add maxConnections to SchemaIO field builder and expose it in xlang wrappers

[Abacn]

What needs to happen?

A maxConnections parameter has been added to JDBCIO (#24851) and the schemaio based xlang wrapper has not yet support it (expansion service, python, go, etc, see #25062 for context). This task aims to add support of this parameter to these wrappers.

Issue Priority

Priority: 2 (default / most normal work should be filed as P2)

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[Abacn]

Fixed by #25824