Strict validation demands web-auth fields even when the web UI is disabled

[CybotTM]

Turning on enable-strict-validation fails a config that does not use the web UI, because web-password-hash and web-secret-key are reported as required.

Reproduction

[global]
  enable-strict-validation = true

[job-local "hello"]
  schedule = @every 30s
  command = echo hi

$ ofelia validate --config=strict.ini
configuration validation failed:
  config validation error for field 'web-password-hash': is required (value: )
  config validation error for field 'web-secret-key': is required (value: )

No [global] enable-web is set, so there is no web UI and no reason to demand credentials for it.

Why it matters

It makes strict validation impractical to adopt: the operator most likely to turn it on — someone who wants their config checked — is met with errors about a feature they are not using. The workaround is to leave strict validation off, which is how the schedule problem in #773 stays invisible.

Note the two issues compound: strict validation is the thing that would catch an unparsable schedule, and this is a reason not to enable it.

Expected

The web-auth fields should be required only when the web UI is enabled and authentication is switched on.

Found while adding exit-code tests in #771.