Adds "Spikes" to iteration strategies

Closes: Product#3043 (closed)

Why is this change being made?

We use the term spike (example 2) (example 3), technical investigation (example 2) and technical evaluation in multiple places interchangeably. We should document one term centrally and reference it consistently.

Approvals

As this MR makes changes to a lot of team pages for which I am not a part of nor the DRI, I'd like to get the approval from the respective DRI(s) for the pages where cross-links have been added.

• The intent of the issue has been satisfied via the added iteration strategy of "Spikes" to the product process page @kencjohnston
• Spikes cross-link added to product development flow page @fseifoddini
• Spikes cross-link added to the Distribution team page @mendeni
• Spikes cross-link added to the Pipeline Authoring team page @marknuzzo
• Spikes cross-link added to the Monitor team page @crystalpoole
• Spikes cross-link added to the Testing team page @shampton

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this change to the correct DRI(s)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR.
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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