Remove json serialization for notify validation

[dmzoneill]

SUMMARY

For the webhook notification, the start body only accepts variables whom transpose to json dict.
E.g : {{job_metadata}} =

{ ..... } 

All other variables such as {{job.id}} which are primitives (int, str, float, etc) do not pass the validation.
They are not dict type and the below check does not allow {{job.scm_reivsion}} etc as requested by #14410

if not isinstance(potential_body, dict):

This patch loosens up this validation to just check for jinja template exception.

related: #14410

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• API

[chrismeyersfsu]

s/gace/gave/

[chrismeyersfsu]

Wow, nice find. How did this ever work? I wonder if we expected the user to manually construct a valid json

i.e.

{
  "my_job_revision": "{{ job.scm_revision }}"
}

vs.

{{ job.scm_revision }}

I reckon this would make it so we support a wider range of webhook servers on the other end .. but that isn't true because we expect the payload to be a JSON. So it's not like the user can go construction xml for a soap request (warning, I don't know what a soap request really looks like).

<xml>
<my_job_revision>{{ job.scm_revision }}</my_job_revision>
</xml>

/end ramble