Refactor ec2_transit_gateway_* modules (ansible-collections#2158)

SUMMARY

Refactor ec2_transit_gateway and ec2_transit_gateway_info modules

common code moved to module_utils ansible-collections#2325
ISSUE TYPE

Bugfix Pull Request
Docs Pull Request
Feature Pull Request
New Module Pull Request

COMPONENT NAME

ec2_transit_gateway
ec2_transit_gateway_info
ADDITIONAL INFORMATION

Reviewed-by: GomathiselviS <gomathiselvi@gmail.com>
Reviewed-by: Alina Buzachis
Reviewed-by: Mandar Kulkarni <mandar242@gmail.com>
Reviewed-by: Bikouo Aubin

This commit was initially merged in https://github.com/ansible-collections/community.aws
See: ansible-collections/community.aws@fc782d2