chore: Add contribution ladder

[sajayantony]

Signed-off-by: Sajay Antony [email protected]

Description

What this PR does / why we need it:

This add the contribution ladder template for the Ratify project and is based of https://github.com/cncf/project-template/blob/main/CONTRIBUTING.md

The current template outlines only a subset of roles.

/cc @bridgetkromhout @akashsinghal @toddysm @susanshi @binbin-li

[sajayantony]

This PR might sit in draft form for a while since folks are ironing out definitions in related projects.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (839a83b) 51.72% compared to head (68bc554) 51.72%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #560   +/-   ##
=======================================
  Coverage   51.72%   51.72%           
=======================================
  Files          61       61           
  Lines        3555     3555           
=======================================
  Hits         1839     1839           
  Misses       1529     1529           
  Partials      187      187           

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