Consume depth flag of vendir in git fetch section of app/package spec

[rohitagg2020]

Describe the problem/challenge you have
In the gitops scenario, if the git repo is very huge it takes lot of time in the fetch stage. To make things a bit faster, instead of fetching all the commit history of git, by default, we can fetch only current commit.

Describe the solution you'd like
Add depth as the field in git config of the fetch section and set its value to 1 by default in the code.

Anything else you would like to add:
[Additional information that will assist in solving the issue.]

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