## What changes were proposed in this pull request?
To allow alternatives to serviceaccounts
### Why are the changes needed?
Although we provide some authentication configuration, such as spark.kubernetes.authenticate.driver.mounted.oauthTokenFile, spark.kubernetes.authenticate.driver.mounted.caCertFile, etc.
But there is a bug as we forced the service account so when we use one of them, driver still use the KUBERNETES_SERVICE_ACCOUNT_TOKEN_PATH file, and the error look like bellow:
the KUBERNETES_SERVICE_ACCOUNT_TOKEN_PATH serviceAccount not exists
### Does this PR introduce any user-facing change?
Yes user can now use `spark.kubernetes.authenticate.driver.mounted.caCertFile`
or token file by `spark.kubernetes.authenticate.driver.mounted.oauthTokenFile`
## How was this patch tested?
Manually passed the certificates using `spark.kubernetes.authenticate.driver.mounted.caCertFile`
or token file by `spark.kubernetes.authenticate.driver.mounted.oauthTokenFile` if there is no default service account available.
Closes#24601 from Udbhav30/serviceaccount.
Authored-by: Udbhav30 <u.agrawal30@gmail.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
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