feat(ecs): update application caching agent to store relationships

[piradeepk]

This change updates the application caching agent to store the application name as well as the services associated to that application as relationships. Storing these objects allows the EcsApplicationProvider to be able to query and retrieve all applications and their related services. Improving the search experience and returning the records quicker.

Previously, if users had too many services in their associated aws accounts, the search would time out, and throw an exception.

Tested by using the current logic, to perform multiple application searches (both using the application search and well as the shared search modal), as well as clicking through an application and deploying to ECS. Then deployed these changes and redid the same tests to validate that the previous behaviour continued to work and the search was able to function as expected.

Fixes: spinnaker/spinnaker#6084

[deverton]

Do you need some additional testing on this? We're running into this issue hard as we add more accounts for ECS.

[piradeepk]

@deverton I haven't been able to reproduce the issue locally, which is why we reverted these changes in the last release. Would love to work with you to determine if this resolves the issue for you (and others)!