Add warnings for undesired changes to plugin hook return values

[TheWitness]

Describe the bug

The Cacti plugin API is dependent on plugin authors returning certain structures to be used by other plugin authors. These structures should ALWAYS be returned. Otherwise errors can be thrown by plugins that assume that they are set.

In the event this happens, Cacti should make every effort to detect this and warn the user who can then either correct this issue, or report it to the plugin maintainer.

Expected behavior

Cacti should do a better job of detecting cases where plugin authors are not using good form when authoring plugins.

Screenshots

Below is an example of the new error that will be logged in the case of a chaining event when there is greater than one plugin using the hook function.

[TheWitness]

The WARNINGS above are just an example. Since this plugin was the only plugin calling the hook, it will not generate a warning even though it is using bad form.

[jdcoats]

So after updating, I noticed that the monitor plugin no longer showed the monitor tab. I disabled monitor and re-enabled and got your warnings. So syslog, monitor and weathermap need some love.

2021/09/06 16:24:18 - CMDPHP WARNING: Plugin hook 'syslog_top_graph_refresh' from Plugin 'syslog' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:18 - CMDPHP WARNING: Plugin hook 'weathermap_top_graph_refresh' from Plugin 'weathermap' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:18 - CMDPHP WARNING: Plugin hook 'monitor_top_graph_refresh' from Plugin 'monitor' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:16 - CMDPHP WARNING: Plugin hook 'syslog_top_graph_refresh' from Plugin 'syslog' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:16 - CMDPHP WARNING: Plugin hook 'weathermap_top_graph_refresh' from Plugin 'weathermap' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:14 - CMDPHP WARNING: Plugin hook 'syslog_top_graph_refresh' from Plugin 'syslog' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:14 - CMDPHP WARNING: Plugin hook 'weathermap_top_graph_refresh' from Plugin 'weathermap' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:14 - CMDPHP WARNING: Plugin hook 'monitor_top_graph_refresh' from Plugin 'monitor' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:06 - CMDPHP WARNING: Plugin hook 'syslog_top_graph_refresh' from Plugin 'syslog' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:06 - CMDPHP WARNING: Plugin hook 'weathermap_top_graph_refresh' from Plugin 'weathermap' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:24:06 - CMDPHP WARNING: Plugin hook 'monitor_top_graph_refresh' from Plugin 'monitor' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:23:25 - CMDPHP WARNING: Plugin hook 'syslog_top_graph_refresh' from Plugin 'syslog' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:23:25 - CMDPHP WARNING: Plugin hook 'weathermap_top_graph_refresh' from Plugin 'weathermap' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.
2021/09/06 16:23:25 - CMDPHP WARNING: Plugin hook 'monitor_top_graph_refresh' from Plugin 'monitor' must return the calling array or variable, and it is not doing so. Please report this to the Plugin author.

[TheWitness]

Okay. Let me dig in to these.