[3.0.0] Add deprecation notice for boto support.

[tremble]

SUMMARY

The last of our boto modules have either been migrated to boto3/botocore or are deprecated and slated for removal in release 4.0.0. Add a deprecation notice for the boto support code in module_utils.

ISSUE TYPE

• Docs Pull Request

COMPONENT NAME

module_utils/

ADDITIONAL INFORMATION

$ grep -rl 'boto\.' */aws/{plugins,scripts}/ | grep '\.py'
amazon/aws/plugins/doc_fragments/aws.py
amazon/aws/plugins/module_utils/ec2.py
amazon/aws/plugins/modules/ec2.py
community/aws/plugins/modules/ec2_elb_info.py
community/aws/plugins/modules/iam.py
community/aws/plugins/modules/rds.py
community/aws/scripts/inventory/ec2.py

• amazon.aws.ec2 module - deprecated - removed_in: 4.0.0
• community.aws.ec2_elb_info module - deprecated - removed_in: 3.0.0
• community.aws.iam module - deprecated - removed_in: 3.0.0
• community.aws.rds module - deprecated - removed_in: 3.0.0
• ec2 inventory script - deprecated

[ansible-zuul]

LGTM!