feat(author-jinja): load jinja extensions from plugins

[rahearn]

Types of changes

• Hot fix (emergency fix and release)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation (change which affects the documentation site)
• Breaking change (fix or feature that would cause existing functionality to change)
• Release (develop -> main)

Quality assurance (all should be covered).

• My code follows the code style of this project.
• Documentation for my change is up to date?
• My PR meets testing requirements.
• All new and existing tests passed.
• All commits are signed-off.

Summary

Builds on the proof of concept at #1684 and:

• moves the methods in the previously new ssp_interface into a set of jinja filters. Example switch in use:

{% for party in ssp_interface.get_parties_for_role(ssp.metadata.responsible_parties, "prepared-by") %} becomes
{% for party in ssp.metadata.responsible_parties | parties_for_role("prepared-by", ssp) %}

{{ ssp_interface.safe_retrieval(address, 'addr_lines', []) | join(' ') }} becomes {{ address.addr_lines | as_list | join(' ') }}

• refactors the jinja code into a module to better organize it and avoid some circular dependencies
• enables loading extensions from plugins, searching under: trestle_{plugin_name}.jinja_ext
• updates plugin docs

Key links:

• Add ability to extend jinja functionality with plugins #1719
• Sonar coverage

Before you merge

• Ensure it is a 'squash commit' if not a release.
• Ensure CI is currently passing
• Check sonar. If you are working for a fork a maintainer will reach out, if required.

[butler54]

Hi @rahearn - sorry for the delay. I'll look at this in the next few days :).

[jpower432]

@rahearn Thanks for this submission! Wanted to add some early feedback here. Requesting new source code files (the newly created jinja package in this case) have the updated copyright info. I added a suggestion on one of the files to what this should be updated to.

[butler54]

LGTM - This is really great work. @jpower432's picked up one comment otherwise the only thing that i've seen here which needs to be tidied here is a dangling comment.

[butler54]

This is a nice improvement :)

[butler54]

Think #this needs to be cleaned up.

[jpower432]

LGTM. Thanks for the contribution @rahearn!

[jpower432]

@rahearn Your branch needs to be up to date with the base branch and then it should be good to merge.