{rdbms-connect} Add support to read UTF-8 files with and without BOM

[alanenriqueo]

If a sql file with UTF-8 BOM encoding is passed to the command az postgres flexible-server execute it will fail because its contents are read assuming that the encoding is utf-8. We need to change to utf-8-sig to be able to handle both cases (UTF-8 with/without BOM).

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[yonzhan]

rdbms-connect

[evelyn-ys]

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