Level 3 input and output defences

[kclark-scottlogic]

In level 3. We have the configurable defenses. The hardcoded key words for input and output filtering don't actually relate to anything in level 3 so when these are turned on they are effectively useless.

[chriswilty]

For Level 3, I suggest lake- and water-related keywords, such as:

• Input filtering: lake, loch, lochan, secret, source
• Output filtering: secret

For Sandbox Level, we probably want something like this:

• Input filtering: bonus, passphrase, password, redundant, redundancy, salary, wage
• Output filtering: password, secret

Note that currently we have the same default defences for Level 3 and Sandbox, so these will need to be separated - see backend/src/defaultDefences.ts