add variables to documentation to manage version numbers

[jcstein]

linking #187

[jcstein]

and to avoid things like this 😄 #192

[S1nus]

it might be good to somehow automate updating the tutorial with the latest supported Ignite and cosmos-sdk

[jcstein]

i have this figured out in https://github.com/celestiaorg/docs-vitepress and a demo is here

[jcstein]

this page and component now all use variables!