Handle GKE client WithCredentialsFile deprecation

[stmcginnis]

WithCredentialsFile has been deprecated for security reasons. This updates the code to use the recommended WithAuthCredentialsFile introduced in the v0.258.0 release with the corresponding credential type that was used internally to the deprecated method.

Needed before we can take the update proposed in #38

Closes: #43

[gauravkghildiyal]

Thanks @stmcginnis

/lgtm
/approve

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This pull-request has been approved by: gauravkghildiyal, stmcginnis

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[stmcginnis]

Ah, I misread. The existing library version has WithAuthCredentials but not WithAuthCredentialsFile. It isn't added until v0.258.0. So we need this along with the dependency update for it to pass. I don't have the ability to push to that dependabot branch, but if someone that does wants to cherry-pick this over...

The other option is to move to that version first to be able to move off the deprecated function, then after that update again to the latest one proposed by dependabot. I actually have the ability to do that, so I'll update this PR to make the interim hop for now. Feel free to bypass to go directly to the newer version.

[gauravkghildiyal]

/hold

[aojea]

test are passing, should be ok now to merge?

[gauravkghildiyal]

Yep can merge now.

/lgtm
/unhold