Update Access Monitoring to use generic template

[ASTRobinson]

As per ticket #8359 this PR updates the access-keys-monitoring script to use a generic gov notify template containing only ((subject)) and ((message)) personalisation's (see below screenshot).

The email body and subject are now defined in code and passed to Gov Notify.

Tested locally and emailed received successfully:

[github-actions]

Trivy Scan Success

Show Output

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Trivy will check the following folders:

</details> #### `Checkov Scan` Success
<details><summary>Show Output</summary>

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Checkov will check the following folders:

CTFLint Scan Success

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Setting default tflint config...
Running tflint --init...
Installing "terraform" plugin...
Installed "terraform" (source: github.com/terraform-linters/tflint-ruleset-terraform, version: 0.9.1)
tflint will check the following folders:

Trivy Scan Success

Show Output

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Trivy will check the following folders: