eli-304 - bugfix - amending eventbridge template

[eddalmond1]

Description

Using JSON Encode in eventbridge, where the 'raw' record is being used in Splunk leads to AWS substituting '<' and '>' characters with their unicode string equivalents. This then resulted in the values not being substituted for the actual ones. The change here is to use heredoc string format for the input template.

This looks to be a bug in the way Terraform and AWS interact e.g. hashicorp/terraform-provider-aws#21959

Context

We need the proper log messages to be sent

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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