Default fetch and clone depth to 1

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Description

Default the fetch/clone depth to 1 to reduce the amount of data pulled down during the clone step

Value

There are examples of projects whose full repo size is over 700MB, whereas their depth of 1 is a third of that size. Their clone step currently takes 30 seconds, so reducing that size will have a positive impact on build performance and network usage.

Definition of Done

The default depth for clone/fetch steps is 1. Docs are updated accordingly.

Effort (Optional)

1 day

Impacted Personas (Optional)

users will benefit mostly.
one caveat is that this could increase cpu load on the github servers, so need to confirm with those admins about the change.