Add support for truncating plugin output to specified size

[atc0005]

Overview

Make this behavior opt-in.

Allow specifying custom cutoff size (e.g., support older monitoring instances).

Allow also truncating to a default value (current Nagios plugin output length restriction is 8192 bytes).

References

• https://github.com/atc0005/go-nagios/issues/251
• Nagios max plugin output length
  • https://github.com/NagiosEnterprises/nagioscore/blob/a30a89e0a493da49416e32ed770e294b1fe800f5/include/nagios.h#L274-L280

[atc0005]

Maybe add separate support for determining whether the plugin output accumulated thus far is approaching the cutoff?

Maybe useful to provide methods that allow appending to an output buffer vs accumulating locally and setting directly against LongServiceOutput and ServiceOutput fields.

A variation of the methods could return either the space remaining or whether a specific percentage has been reached?