Align error code & definition as specified in Commonalities 0.5

[bigludo7]

What type of PR is this?

Add one of the following kinds:

• enhancement/feature

What this PR does / why we need it:

Commonalities v0.5 alignement:

• remove 500 & 503 codes
• redefine the error structure

Which issue(s) this PR fixes:

Fixes #67

Special notes for reviewers:

Changelog input

 release-note
- Remove errors 500 & 503 (No impact on API client code)
- Aligne the error definition as specified in Camara commonalities (No impact on API client code)

Additional documentation

This section can be blank.

docs

[jgarciahospital]

LGTM