feat(Templates): render text field as jinja2 template

[herrtxbias]

Fixes #593

[Phhere]

Hi,

the feature does not work as planned.
When you try to create an maintenance or inciecent from such an template, the we get an exception

ValueError at /dashboard/maintenances/add/

"<Maintenance: >" needs to have a value for field "id" before this many-to-many relationship can be used.

Request Method: 	GET
Request URL: 	http://127.0.0.1:8001/dashboard/maintenances/add/?template=1
Django Version: 	4.2.13
Exception Type: 	ValueError
Exception Value: 	

"<Maintenance: >" needs to have a value for field "id" before this many-to-many relationship can be used.

Exception Location: 	/opt/statuspage/venv/lib/python3.11/site-packages/django/db/models/fields/related_descriptors.py, line 1022, in __init__