python.d: merge user/stock plugin configuration files

[ilyam8]

Summary

This PR changes loading stock/user python.d.plugin configuration files logic (python.d.conf).

❗ yes, the changes concern only plugin configuration loading, not its modules (e.g.: apache.conf, mysql.conf)

Current:

• load user config if it exists.
• if not load stock config.

After this PR:

• load user config if it exists.
• load stock config file.
• merge user into stock.

In addition, python.d.plugin no longer fails to start if there are any problems on loading configuration files (e.g.: invalid YAML syntax), it starts and uses internal defaults.

---

Motivation: the feature/change was requested on our forum. See the following topics:

• override-config-files
• local-support-for-on-off-plugins.

Component Name

collectors/python.d.plugin

Test Plan

Manual tests 😐

• check that user config get merged into stock
• check the plugin doesn't stop if there are any errors during config loading (invalid YAML syntax)

Additional Information

[netdata-community-bot]

This pull request has been mentioned on Netdata Community. There might be relevant details there:

https://community.netdata.cloud/t/local-support-for-on-off-plugins/1003/11

[netdata-community-bot]

This pull request has been mentioned on Netdata Community. There might be relevant details there:

https://community.netdata.cloud/t/override-config-files/1342/14

[k0ste]

Sorry for late reply, just confirms that feature works as expected 🤝
Support for '.local' pythond.d.conf also added in netdata ansible-role here: k0ste/ansible-role-netdata@ed04600
Works fine with CentOS8-Stream EPEL packages 🎉