Resolve Traps OIDs to names

[FlorianVeaux]

With this PRs traps payload format has been refactored:

1. The source and service are now snmp-traps.
2. The traps variables are now stored under .raw_variables instead of .variables.
3. Traps payloads are enriched thanks to an OIDResolver interface that loads traps_db files located in snmp.d/traps_db/

How to test:

1. If not shipped already, you can download this database file and place it under snmp.d/traps_db/ directory (you can leave it compressed).
2. Start the agent with the following configuration in datadog.yaml

logs_enabled: true
snmp_traps_enabled: true
snmp_traps_config:
  port: 9162
  community_strings:
    - 'public'
    - 'default'

3. Send traps on port 9162 with the command snmptrap -v2c -c public localhost:9162 '' IF-MIB::linkDown ifIndex i 12 ifAdminStatus i 1 ifOperStatus i 2
4. Look on Datadog logs and check that the received traps payload have been correctly formatted and enriched.

[FlorianVeaux]

Prevent flakiness

[AlexandreYang]

(no blocking for this PR since it was already there)

Do we need to report the SNMP version ?

Not sure if that's useful info, it's more related to the kind of credentials used (v2 community string, v3 user model) and not really part of the trap information. Also, a same device can support both v2 community string and v3 user model.

[FlorianVeaux]

Didn't want to change it in this PR. Do you think we should remove it?
The version doesn't provide I agree but it doesn't harm to have it

[AlexandreYang]

Same as #10934 (comment)