Creating a variable larger that 4000 characters results in validation error

Issue Summary

This is reproducible on Data Center: (yes)

Steps to Reproduce

GUI:

1. Go to the global variables admin pane.
2. Create a variable with a value larger than 4000 characters.

REST API:

1. Enable admin rest endpoints
2. Create a variable with a value larger than 4000 characters via REST API.

Expected Results

Bamboo should allow the creation of variables with a size of 65535 bytes (UTF-8 encoding)

Actual Results

Length exceeds 4000 characters.

Bamboo displays a validation error

Workaround

Currently, there is no known workaround for this behaviour. A workaround will be added here when available