fix: update gateway instructions

[loujaybee]

Description

• Update gateway instructions from repo to main documentation
• Removed markdown documentation

Related Issue(s)

N/A

How to test

• Set JetBrains preferences
• Open workspace
• Links should be as expected (link to docs, not to GitHub / markdown)

Release Notes

NONE

Documentation

N/A

[codecov]

Codecov Report

Merging #8421 (c9f2c81) into main (343ae26) will decrease coverage by 25.25%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main   #8421       +/-   ##
==========================================
- Coverage   32.85%   7.59%   -25.26%     
==========================================
  Files          33      31        -2     
  Lines        4745    2172     -2573     
==========================================
- Hits         1559     165     -1394     
+ Misses       3068    2004     -1064     
+ Partials      118       3      -115     

Flag	Coverage Δ
components-gitpod-cli-app	11.17% <ø> (ø)
components-local-app-app-darwin-amd64	?
components-local-app-app-darwin-arm64	?
components-local-app-app-linux-amd64	?
components-local-app-app-linux-arm64	?
components-local-app-app-windows-386	?
components-local-app-app-windows-amd64	?
components-local-app-app-windows-arm64	?
components-ws-manager-app	?
install-installer-raw-app	4.58% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
components/local-app/pkg/auth/pkce.go
components/ws-manager/pkg/manager/metrics.go
components/ws-manager/pkg/manager/create.go
components/ws-manager/pkg/manager/status.go
...s/ws-manager/pkg/manager/internal/grpcpool/pool.go
components/ws-manager/pkg/manager/annotations.go
components/ws-manager/pkg/manager/manager.go
components/ws-manager/pkg/manager/monitor.go
components/ws-manager/pkg/manager/imagespec.go
...omponents/ws-manager/pkg/manager/pod_controller.go
... and 18 more

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[akosyakov]

closed, because branch name is too long, see #8432 instead