TT-18145: increaase IAM session for first time pruning

[olamilekan000]

Description

The default OIDC session expired mid-run; the workflow now
requests a 6-hour session (IAM role max raised to match).

Jira Ticket: TT-18145

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Chore / documentation / template sync

Verification & Testing

• I have run local unit tests (go test ./policy/...) and they passed.
• I have generated policy outputs locally (go run . policy gen) and verified the rendered files.
• I have verified the changes in target downstream repositories (e.g. tyk, tyk-analytics).

Command(s) used for testing:

# Example: go run . policy gen /tmp/output --repo tyk --branch master

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings