fix: DBTP-1563 - Use iam_role_policy instead of deprecated inline policies

[JohnStainsby]

Addresses https://uktrade.atlassian.net/browse/DBTP-1563

Fix these warnings every time we run a terraform command:

│ Warning: Argument is deprecated
│ 
│   with module.extensions.module.elasticache-redis["demodjango-redis"].aws_iam_role.conduit_ecs_task_role,
│   on .terraform/modules/extensions/elasticache-redis/main.tf line 88, in resource "aws_iam_role" "conduit_ecs_task_role":
│   88: resource "aws_iam_role" "conduit_ecs_task_role" {

---

Checklist:

Title:

• Scope included as per conventional commits
• Ticket reference included (unless it's a quick out of ticket thing)

Description:

• Link to ticket included (unless it's a quick out of ticket thing)
• Includes tests (or an explanation for why it doesn't)
• Includes any applicable changes to the documentation in this code base
• Includes link(s) to any applicable changes to the documentation in the DBT Platform Documentation (can be to a pull request)

Tasks:

• Trigger the pull request regression tests for this branch and confirm that they are passing

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.68%. Comparing base (3389320) to head (adbcbb5).

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #347   +/-   ##
=======================================
  Coverage   81.68%   81.68%           
=======================================
  Files           7        7           
  Lines         868      868           
=======================================
  Hits          709      709           
  Misses        159      159           

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[WillGibson]

😍