enh(api): Added Rest API to display and update the default configuration of the Centreon proxy

[callapa]

Description

Added a new REST API to allow to display and update the default configuration of the Centreon proxy.

Type of change

• Patch fixing an issue (non-breaking change)
• New functionality (non-breaking change)
• Breaking change (patch or feature) that might cause side effects breaking part of the Software
• Updating documentation (missing information, typo...)

Target serie

• 2.8.x
• 18.10.x
• 19.04.x
• 19.10.x
• 20.04.x (master)

How this pull request can be tested ?

To get the default configuration:
curl -X GET -H 'X-AUTH-TOKEN: my_token' http://my_centreon/centreon/api/beta/configuration/proxy

To update the default configuration of the Centreon proxy:
curl -X POST -H 'Content-Type: application/json' -H 'X-AUTH-TOKEN: my_token' http://my_centreon/centreon/api/beta/configuration/proxy -d '{"url": "my_proxy_url", "port": 1234, "user": "my_user", "password": "my_password"}'

Checklist

Community contributors & Centreon team

• I followed the coding style guidelines provided by Centreon
• I have commented my code, especially new classes, functions or any legacy code modified. (docblock)
• I have commented my code, especially hard-to-understand areas of the PR.
• I have made corresponding changes to the documentation.
• I have rebased my development branch on the base branch (master, maintenance).

Centreon team only

• I have made sure that the unit tests related to the story are successful.
• I have made sure that unit tests cover 80% of the code written for the story.
• I have made sure that acceptance tests related to the story are successful (local and CI)