Refactor notification mechanism

[johananl]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR refactors the notification mechanism. Here is what it does specifically:

• Replace the global notifications map with a new Report type.
• One local Report instance is created in ToGatewayAPIResources().
• A *Report pointer is passed to each provider/emitter constructor.
• Each provider/emitter calls Report.Notifier() to create its own provider/emitter-scoped NotifyFunc and stores this function as a property.
• Conversion code can now emit notifications by calling a package-scoped notify() function.

There are no user-facing changes -- this is an implementation change only. The size of the PR is largely due to repetitive replacements of the "instrumentation" everywhere.

Which issue(s) this PR fixes:

Fixes #340

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
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[johananl]

/test pull-ingress2gateway-e2e

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: johananl, LiorLieberman

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[johananl]

We have no character limit on the notification message which can mess up the tables when the terminal isn't big enough.

I'm fine with either format. The colored box design was done using an slog handler. I can look into "porting" the visuals without reintroducing the logging library (since we've agreed to keep notifications as distinct from logs).

[Stevenjin8]

@johananl makes sense.
/lgtm

[johananl]

I'm porting the design from #341.

[Stevenjin8]

/unhold
/lgtm