Add support for streams (TCP and UDP loadbalancing)

PR progress checklist (to be filled in by reviewers)

[ ] Changes to documentation are appropriate (or tick if not required)
[ ] Changes to tests are appropriate (or tick if not required)
[ ] Reviews completed

What type of PR is this?

Primary type

[ ] [build] Changes related to the build system
[ ] [chore] Changes to the build process or auxiliary tools and libraries such as documentation generation
[ ] [ci] Changes to the continuous integration configuration
[x] [feat] A new feature
[ ] [fix] A bug fix
[ ] [perf] A code change that improves performance
[ ] [refactor] A code change that neither fixes a bug nor adds a feature
[ ] [revert] A change used to revert a previous commit
[ ] [style] Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc.)

Secondary type

[ ] [docs] Documentation changes
[ ] [test] Adding missing or correcting existing tests

Does this PR introduce a `BREAKING CHANGE`?

No.

Related issues and/or pull requests

N/A

Describe the changes you're proposing

Currently the formula does not have support for streams (TCP and UDP loadbalancing), and putting it in the nginx.conf file doesn't work due to key conflicts (the server key is used for the main config, but also used by streams). Either way, I couldn't get it right and it seems a bit cleaner in my opinion to have streams working like snippets instead of putting everything in the main config.

see https://docs.nginx.com/nginx/admin-guide/load-balancer/tcp-udp-load-balancer/

Pillar / config required to test the proposed changes

I exactly copied and pasted the snippets functionality and changed it to streams, and added some defaults to the map file. I don't know how to test it, but am willing to learn. It's working for my use case so far, for what it's worth

Debug log showing how the proposed changes work

Documentation checklist

[ ] Updated the README (e.g. Available states). ---> N/A
[x] Updated pillar.example.

Testing checklist

[ ] Included in Kitchen (i.e. under state_top).
[ ] Covered by new/existing tests (e.g. InSpec, Serverspec, etc.).
[ ] Updated the relevant test pillar.

Additional context

I've not done a pull request before and I do not understand how the formulas are tested, please guide me in the right direction if there are mistakes.

saltstack-formulas / nginx-formula