Update test_create_portal_metadata to use assertProjectReadmeContent

[nozomione]

Context

Parent issue: #708

Feature branch: feature/portal-metadata-command

With the merge of feature/consolidate-readmes into dev, we introduced a new method for testing readme file correctness, assertProjectReadmeContent. This method replaced the previous assertProjectReadmeContains, which checked for specific strings within readme files. The new method performs a line-by-line comparison to make sure the format and content of the expected and output readme files are identical.

Problem or idea

The test for the portal metadata readme file is still using the outdated assertProjectReadmeContains method. To align with the new changes and verify the accuracy of the portal metadata readme file, we need to adjust the create_portal_metadata management command test to use the new assertProjectReadmeContent method.

Solution or next step

1. Generate the portal metadata readme file in test_data/readmes
2. Add placeholders TEST_TODAYS_DATE and PROJECT_ID_{i} to the newly generated readme file
3. Update test_create_portal_metadata to use assertProjectReadmeContent and confirm the correctness of the portal metadata readme file