Generate JSON responses inside the database

[waldiTM]

What this PR does / why we need it:
PostgreSQL can actually generate JSON objects from scratch and aggregate existing JSON fields as well into lists. While it might not be faster, it frees the currently single threaded web server.

Also we need to use JSON instead of JSONB. The queries run about 50% faster and we don't manipulate JSON any further in the database anyway.

[waldiTM]

Benchmark:

Assembling JSON in web service: 510ms

Document Path:          /rest/json/cves/2.0+deb?virtualMatchString=cpe:2.3:o:debian:debian_linux:*:*:*:*:*:*:*:*
Document Length:        14515234 bytes

Concurrency Level:      1
Time taken for tests:   51.024 seconds
Complete requests:      100
Failed requests:        0
Total transferred:      1451538800 bytes
HTML transferred:       1451523400 bytes
Requests per second:    1.96 [#/sec] (mean)
Time per request:       510.237 [ms] (mean)
Time per request:       510.237 [ms] (mean, across all concurrent requests)
Transfer rate:          27781.58 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.0      0       0
Processing:   405  510  31.6    510     590
Waiting:      389  496  31.7    495     574
Total:        405  510  31.6    510     590

Percentage of the requests served within a certain time (ms)
  50%    510
  66%    522
  75%    530
  80%    536
  90%    551
  95%    564
  98%    579
  99%    590
 100%    590 (longest request)

Assembling JSON in database: 142ms

Document Path:          /rest/json/cves/2.0+deb?virtualMatchString=cpe:2.3:o:debian:debian_linux:*:*:*:*:*:*:*:*
Document Length:        15263315 bytes

Concurrency Level:      1
Time taken for tests:   14.195 seconds
Complete requests:      100
Failed requests:        0
Total transferred:      1526347700 bytes
HTML transferred:       1526331500 bytes
Requests per second:    7.04 [#/sec] (mean)
Time per request:       141.947 [ms] (mean)
Time per request:       141.947 [ms] (mean, across all concurrent requests)
Transfer rate:          105008.83 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.0      0       0
Processing:   124  142   9.4    140     191
Waiting:      110  126   9.0    124     170
Total:        124  142   9.4    140     191

Percentage of the requests served within a certain time (ms)
  50%    140
  66%    141
  75%    142
  80%    143
  90%    150
  95%    163
  98%    180
  99%    191
 100%    191 (longest request)

Interestingly the output get's quite a bit larger.

This query is also the worst case, returning almost 25k entries at once.