Allow passing k/v pairs to a custom J2 template

[vachillo]

• I have read and agree to the contributing guidelines.

Is your feature request related to a problem? Please describe.
I have custom J2 templates that i would like to use, but i have no way to pass custom k/v pairs without overriding the entire class

Describe the solution you'd like
I want to pass a dict to a Tool/Engine that use J2 templates that i can use to pass in k/v pairs to render to my custom template

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[collindutter]

This should be implemented through the following:

1. Add task: self to BaseTask.full_context.
2. Add context: self.full_context as arguments to all Task uses of J2.render.