Created new flag --notifications-output-file to specify where to output notifications

[Devaansh-Kumar]

What type of PR is this?

/kind feature

What this PR does / why we need it:
This PR adds a new flag called --notifications-output-file to specify where to output notifications. If the flag is not present, then notifications are send to stdout.

Which issue(s) this PR fixes:

This pull request addresses part of the issue described in #131

Does this PR introduce a user-facing change?:

Added flag `--notifications-output-file`.

/cc @mlavacca @LiorLieberman

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Devaansh-Kumar
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[k8s-ci-robot]

Hi @Devaansh-Kumar. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[k8s-ci-robot]

PR needs rebase.

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