Add DCO requirements and updated code of conduct

[willtsai]

Issue reference: dapr/docs#2039

Description

Add DCO requirements and updated code of conduct. Content inspired and borrowed from https://github.com/kedacore/keda/blob/main/CONTRIBUTING.md#developer-certificate-of-origin-signing-your-work

Issue reference

dapr/docs#2039

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Unit tests passing
• End-to-end tests passing
• Extended the documentation / Created issue in the https://github.com/dapr/docs/ repo: dapr/docs#[issue number]
• Specification has been updated / Created issue in the https://github.com/dapr/docs/ repo: dapr/docs#[issue number]
• Provided sample for the feature / Created issue in the https://github.com/dapr/docs/ repo: dapr/docs#[issue number]

[codecov]

Codecov Report

Merging #235 (59b4c32) into main (831379c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #235   +/-   ##
=======================================
  Coverage   63.14%   63.14%           
=======================================
  Files          23       23           
  Lines        1305     1305           
=======================================
  Hits          824      824           
  Misses        405      405           
  Partials       76       76           

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