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.

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