Add 0005 to "Best Practices for CNF Developers" doc

[lixuna]

Summary

0005-single-concern-per-container.md has been merged in https://github.com/cncf/cnf-wg/pull/267

This best practice is under the Microservices Category

Please add the reference link for 0005 to:

• Best Practices for CNF Developers doc https://github.com/lfn-cnti/bestpractices/blob/main/doc/best_cnf_dev.md
• Under 3.0 Microservices Category https://github.com/lfn-cnti/bestpractices/blob/main/doc/best_cnf_dev.md#30-microservices

References

#242

#267

https://github.com/cnti-testcatalog/testsuite/blob/main/USAGE.md#microservice-tests