chore(backstage): Adding support for backstage

[montabot]

Description

What?

As we open up for the Backstage developer portal (backstage.staging.monta.app) we require some files to be in your repo. This includes:

• catalog-info.yaml: We use this to index your repo in backstage with the required config
• mkdocs.yaml: We use this file to generate TechDocs, from the docs folder
• .docs dir: This is where we will store documentation for the code in the future, in case it isn't already.

Why?

Backstage is a developer portal, you can read more about it on the notion page: https://www.notion.so/montaapp/Backstage-4e9f3e658dc64c85847290ba333876d9?pvs=4

Context

In the context of cataloging every service we have on Backstage.

There are some things that have to be changed manually, these changes can be found in the catalog-info.yaml:

1. metadata.labels.tier
2. metadata.links. → set Slack url
3. metadata.links. → set Notion url
4. metadata.links. → set Grafana url
5. spec.lifecycle → experimental, production, deprecated

These changes are nice to have but not super necessary, just i you have spare time to make a commit before merging the PR.

Type of change

I'm only adding files.