make config field mandatory on sinks creation

[mclcavalcante]

Make sink config mandatory on sink creation and check if it has the minimum amount of keys to create

*Plus make some unit tests more readable

[codecov-commenter]

Codecov Report

Base: 4.91% // Head: 64.00% // Increases project coverage by +59.08% 🎉

Coverage data is based on head (c2f7a20) compared to base (7ef874b).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #2112       +/-   ##
============================================
+ Coverage     4.91%   64.00%   +59.08%     
============================================
  Files           15       61       +46     
  Lines         1057     4601     +3544     
============================================
+ Hits            52     2945     +2893     
- Misses        1005     1656      +651     

Impacted Files	Coverage Δ
fleet/postgres/agent_groups.go	81.88% <100.00%> (ø)
sinks/api/http/requests.go	98.30% <100.00%> (ø)
sinks/postgres/sinks.go	73.41% <100.00%> (ø)
agent/backend/pktvisor/pktvisor.go
agent/otel/otlpmqttexporter/config.go
agent/backend/pktvisor/scrape.go
agent/otel/otlpmqttexporter/factory.go
agent/heartbeats.go
agent/otel/pktvisorreceiver/factory.go
agent/otel/pktvisorreceiver/receiver.go
... and 69 more

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[lpegoraro]

LGTM