api: Added v1/status/flags endpoint. (#3864)
Endpoint URL: /api/v1/status/flags
Example Output:
```json
{
"status": "success",
"data": {
"alertmanager.notification-queue-capacity": "10000",
"alertmanager.timeout": "10s",
"completion-bash": "false",
"completion-script-bash": "false",
"completion-script-zsh": "false",
"config.file": "my_cool_prometheus.yaml",
"help": "false",
"help-long": "false",
"help-man": "false",
"log.level": "info",
"query.lookback-delta": "5m",
"query.max-concurrency": "20",
"query.timeout": "2m",
"storage.tsdb.max-block-duration": "36h",
"storage.tsdb.min-block-duration": "2h",
"storage.tsdb.no-lockfile": "false",
"storage.tsdb.path": "data/",
"storage.tsdb.retention": "15d",
"version": "false",
"web.console.libraries": "console_libraries",
"web.console.templates": "consoles",
"web.enable-admin-api": "false",
"web.enable-lifecycle": "false",
"web.external-url": "",
"web.listen-address": "0.0.0.0:9090",
"web.max-connections": "512",
"web.read-timeout": "5m",
"web.route-prefix": "/",
"web.user-assets": ""
}
}
```
Signed-off-by: Bartek Plotka <bwplotka@gmail.com>