Stop relying on manifest.json to validate spec.yaml

[iliakur]

What does this PR do?

1. Don't load manifest.json when validating the config and models we genreate from spec.yaml.
2. Drop requirement for name field in spec.yaml. We don't use it anywhere.

! Update: I missed part of this and had to implement that in a follow-up PR!

Motivation

We're moving manifest.json to Publishing Platform, so we can't rely on it being present.
This is one step to reduce our dependency on it.
Without this change contributors using Publishing Platform will have failing validations.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.47%. Comparing base (617cdb8) to head (1c211a9).
Report is 22 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
confluent_platform	?
datadog_checks_dev	77.59% <100.00%> (-0.05%)	⬇️
hive	?
hivemq	?
hudi	?
ignite	?
jboss_wildfly	?
kafka	?
presto	?
solr	?
tomcat	?
weblogic	?

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Review from steveny91 is dismissed. Related teams and files:

• agent-integrations
  • datadog_checks_dev/tests/tooling/configuration/test_load.py