Performance of generating /configs/list response

[tkaik]

Describe the bug
For large AET databases, getting response from /configs/list endpoint takes a very long time and consumes a lot of system resources (RAM, CPU) which might heavily impact performance of running suites in the system.

• Version used: AET 3.2.2

To Reproduce
Steps to reproduce the behavior:

1. Prepare AET environment with large database (e.g. at least 100 GB in size / few hundreds of suites, each with few hundred versions)
2. Go to /config/list
3. Wait for reponse

Expected behavior
Response should be returned quickly even for large databases. Response content may be limited to last X versions of report for each suite, instead of always returning every availalbe raport URL.

Additional context
Currently /configs/list endpoint is building full HTML response with StringBuilder. Consider chaning this approach. It also may be worth to check if executed DB queries are using indexes.