docs: adds RATIONALE.md with section on why TinyGo

[codefromthecrypt]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

This reverse documents a decision we made about TinyGo.

Which issue(s) this PR fixes:

NONE

Special notes for your reviewer:

documents the most important part of https://github.com/kubernetes-sigs/kube-scheduler-wasm-extension/pull/6

Does this PR introduce a user-facing change?

NONE

What are the benchmark results of this change?

N/A

[codefromthecrypt]

ps you may wonder why have RATIONALE.md vs a separate website etc. For a fast moving project, it is more coherent to have changes self-contained. For example, a decision and its rationale in the same commit ideally. When things settle down, we can easily harvest these docs to a separate web page, if it is required to host them externally. Meanwhile, it encourages documentation of decisions otherwise left to PR comments because the follow-up overhead penalty adds friction and work.

[ffromani]

/cc

[codefromthecrypt]

once this is in, I'll rebase https://github.com/kubernetes-sigs/kube-scheduler-wasm-extension/pull/25 and add the rationale for nottinygc as that is also not intuitive unless you had our experiences.

[kerthcet]

part of https://github.com/kubernetes-sigs/kube-scheduler-wasm-extension/issues/14

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: codefromthecrypt, kerthcet

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