ENG-1292 make restore lambda arns available as outputs, and update docs

[hirra-farooq]

Description

The backup source module can optionally create lambdas used during restoration which have the ability to:

• trigger copy of a s3 recovery point from destination to source account
• trigger a restore of a recovery point to s3
  This PR makes the arn of these lambdas available as outputs if created

Context

Allows consumers to directly get the arn of the created lambdas through tf

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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Sensitive Information Declaration

To ensure the utmost confidentiality and protect your and others privacy, we kindly ask you to NOT including PII (Personal Identifiable Information) / PID (Personal Identifiable Data) or any other sensitive data in this PR (Pull Request) and the codebase changes. We will remove any PR that do contain any sensitive information. We really appreciate your cooperation in this matter.

• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.