Add docs for 'Topology Spread Constraint' support in K8S build pods.

[dewan-ahmed]

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Description

• Please describe your changes: This PR adds docs for 'Topology Spread Constraint' support in K8S build pods.
• Jira/GitHub Issue numbers (if any): https://harness.atlassian.net/browse/CI-14248
• Preview links/images (Internal contributors only): to be added

@nofarblue this PR adds to FAQ. How can I update this new field in the product documentation? i.e. a page like this?

PR lifecycle

PRs must meet these requirements to be merged:

• Successful preview build.
• Code owner review.
• No merge conflicts.
• Release notes/new features docs: Feature/version released to at least one prod environment.

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