Docs: Add transformations documentation (#24597)

* Create transformations.md

* Update transformations.md

* Create calculations-list.md

* Update transformations.md

* Update menu.yaml

* Update transformations.md

* Update calculations-list.md

* updated menu

* Delete text.md

Deleted old text panel topic

* Update transformations.md

* added content

* Update transformations.md

* Update whats-new-in-v7-0.md

* Update transformations.md

* Update docs/sources/panels/transformations.md

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

* Update docs/sources/panels/transformations.md

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

* Update docs/sources/panels/transformations.md

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

* Update docs/sources/panels/calculations-list.md

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

* Update docs/sources/panels/transformations.md

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

* Update transformations.md

* fixed broken links

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

docs/sources/features/panels/text.md

@@ -1,23 +0,0 @@
-+++
-title = "Text"
-keywords = ["grafana", "text", "documentation", "panel"]
-type = "docs"
-aliases = ["/docs/grafana/latest/reference/alertlist/"]
-[menu.docs]
-name = "Text"
-parent = "panels"
-weight = 4
-+++
-
-
-# Text Panel
-
-The text panel lets you make information and description panels etc. for your dashboards. There are three modes you can write in: markdown, HTML or text.
-
-## Text Options
-
-{{< docs-imagebox img="/img/docs/v45/text-options.png" max-width="600px" class="docs-image--no-shadow">}}
-
-1. **Mode**: Here you can choose between markdown, HTML or text.
-2. **Content**: Here you write your content.
-