Make the "we can't communicate with your server" error more descriptive

Issue Summary

This is reproducible on Data Center: yes

Steps to Reproduce

The error "We can't communicate with your server" can occur in JCMA, CCMA, as well as Bitbucket migrations for a number of reasons including database connectivity or performance issues and network issues (not able to connect to the cloud site or cloud migration services).

This error can, for example, prevent migration plans from being created or apps from being assessed. 

Example: 

1. Block network connectivity from the source application server to the cloud site or the internet
2. Try to create and run a migration plan 

Expected Results

It would help if the error message was more descriptive so that users knew what to check. For example, if the error is related to the database, then the error message could point to this. 

Actual Results

You'll receive this generic error message:

"We can't communicate with your server"

 
The below example exceptions can be thrown in the application log file:

2024-03-17 13:38:27,384 WARN [ForkJoinPool.commonPool-worker-3] [agent.service.impl.MigrationAppAggregatorService] getAggregatedAppData Failed to talk to app-aggregator. Returning default values. Error code: 404
 -- referer: https://confluence.server.com/admin/migration.action | url: /rest/migration/latest/app | traceId: 753e1d3c234d85ac | userName: admin.user

referer: https://confluence.server.com.au/admin/migration.action | url: /rest/migration/latest/plan | traceId: 6f3f96123d9fad17 | userName: admin.user
com.atlassian.migration.agent.okhttp.HttpServiceException: Unauthorized

Workaround

The resolution can be a number of things depending on the root cause. If you need assistance on this error, please reach out to support.