feat: Support get CREDENTIAL_ENV_NAME from properties

[tisonkun]

This closes #781.

Signed-off-by: tison [email protected]

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Fixes #781 ☕️

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[tisonkun]

ping @Neenu1995 @meltsufin any updates?

[meltsufin]

@tisonkun Which client library are you using?

[tisonkun]

@meltsufin it's the BigQuery client.

[tisonkun]

Thank you!