Low code coverage

We have a Current cove coverage of around 67% which is quite low. we should aim to increase the coverage upto 90%.
Below are the specfic functions and areas of code which remain uncovered and are causing low coverage.

**Base: utils.py**

encode_data
decode_data
send_email
get_url_from_hostname
get_or_create_sqs_queue

**Challenge: aws_utils.py**

register_task_def_by_challenge_pk
create_service_by_challenge_pk
update_service_by_challenge_pk
delete_service_by_challenge_pk
service_manager
start_workers
stop_workers
scale_workers
delete_workers

**admin.py**

start_selected_workers
scale_selected_workers
restart_selected_workers
delete_selected_workers

**admin_filters.py**

lookups
queryset

**Jobs: utils**

is_url_valid
get_file_from_url

**Jobs: aws_utils.py**

generate_aws_eks_bearer_token

**tasks.py**

download_file_and_publish_submission_message

**admin.py**

make_submission_private
change_submission_status_to_cancel

Additionally, I've noticed that some files under the "Scripts/worker" directory have a code coverage of 0%. It would be beneficial to address this and include appropriate tests for these files as well:

**Scripts/worker - remote_submission_worker.py**

download_and_extract_zip_file
load_challenge
extract_challenge_data
process_submission_callback
process_submission_message
extract_submission_data
read_file_content
run_submission

**Scripts/worker - submission_worker.py**

extract_challenge_data
load_challenge
run_submission
process_add_challenge_message

**Scripts/worker - worker_utils.py: (0% coverage)**

**Scripts/worker - rl_submission_worker.py: (0% coverage)**