Add content for templates in vela-tutorials

[jbrockopp]

Description

Original story: go-vela/vela-tutorials#2

Add content for the templates section.

Value

Decrease barrier to entry with templates
Increase clarity around intended use-cases for templates
Create a guide for other organizations to create their own templates

Definition of Done

The tutorials section of this repository contains content.

Effort (Optional)

2 days

Impacted Personas (Optional)

users who use templates

[stale]

This issue has been automatically marked as stale due to no recent activity for the last 60 days.
It will be closed if no further activity occurs in the next 30 days.
Thank you for your contributions!

[plyr4]

theres plenty of content in
https://go-vela.github.io/docs/templates/tutorials/ (could use more instances)
and https://go-vela.github.io/docs/tour/templates/
if we feel the need for more content, more concise issues would be appreciated and helpful

[plyr4]

as an aside, there is a lot of additional content in go-vela/vela-tutorials that could be migrated to the doc-site, lets do that