Document limitation of CI runner acceleration

What does this MR do?

This MR highlights a limitation in the CI runner acceleration feature.

The changes required for the first stage of the pipeline may not have been replicated and verified on the secondary at the time of execution, therefore the clone request is forwarded to the primary site. In most cases, the subsequent stages of the pipeline will be served from the secondary site.

#446176 proposes an enhancement to increase the chance of the first stage clone request is served from the secondary site.

Related issues

CI runner acceleration feature epic: &9779 (closed)

Proposed enhancement: #446176

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