PB-1949 Move tutorials to Tech Docs

This  contains two changes to in the [apitransactional.html](https://data.geo.admin.ch/api/stac/static/spec/v1/apitransactional.html):

1. Add a link to the [Tech Docs](https://sys-docs.int.bgdi.ch/download-data/stac-api/overview.html) on the top of the page.
2. Remove all content that is now also present in the [Tech Docs](https://sys-docs.int.bgdi.ch/download-data/stac-api/overview.html). Replace it with a short description + a link.

I only pointed to the [STAC API Overview page](https://sys-docs.int.bgdi.ch/download-data/stac-api/overview.html) and not to specific subpages, like e.g. [Authentication](https://sys-docs.int.bgdi.ch/docs/stac-api/authentication.html). I thought it does not add a lot of benefit and reduces the risk of outdated links.

Note that the final docs.geo.admin.ch is not live yet but the Terraform code for it is ready and reviewed: geoadmin/infra-terraform-bgdi#1212. So I only merge this when docs.geo.admin.ch is actually online.

To try out how this looks as a website, run this locally:
1. Run `make build-specs`
2. Run `make serve-specs`
3. Open the page at http://127.0.0.1:8090/apitransactional.html.

Author: asteiner-swisstopo

spec/openapi.yaml

@@ -3,10 +3,12 @@ info:
   contact:
     name: API Specification (based on STAC)
     url: http://data.geo.admin.ch/api/stac/v1/
-  description: >-
+  description: |
     This is an OpenAPI definition of the API to query and access federal geodata on
     data.geo.admin.ch. The API is based on the core SpatioTemporal Asset Catalog API specification
     [STAC](http://stacspec.org) and adds two extensions for extended searching possibilities.
+
+    Find tutorials, examples and best practices around the STAC API in the [Tech Docs](https://docs.geo.admin.ch/download-data/stac-api/overview.html).
   title: The SpatioTemporal Asset Catalog API for data.geo.admin.ch
   version: 1.0.0
 servers:

spec/static/assets/service-stac-upload-process.dia

@@ -1958,8 +1958,12 @@ info:
   contact:
     name: API Specification (based on STAC)
     url: http://data.geo.admin.ch/api/stac/v1/
-  description: >-
-    This is an OpenAPI definition of the API to query and access federal geodata on data.geo.admin.ch. The API is based on the core SpatioTemporal Asset Catalog API specification [STAC](http://stacspec.org) and adds two extensions for extended searching possibilities.
+  description: |
+    This is an OpenAPI definition of the API to query and access federal geodata on
+    data.geo.admin.ch. The API is based on the core SpatioTemporal Asset Catalog API specification
+    [STAC](http://stacspec.org) and adds two extensions for extended searching possibilities.
+
+    Find tutorials, examples and best practices around the STAC API in the [Tech Docs](https://docs.geo.admin.ch/download-data/stac-api/overview.html).
   title: The SpatioTemporal Asset Catalog API for data.geo.admin.ch
   version: 1.0.0
 servers: