Chore: Archive 2.6 and 2.7 (legacy branch side)

[lena-larionova]

Description

Moving the 2.6 and 2.7 docs to the legacy-gateway branch.

Sister PR to #8036.

Testing instructions

Preview link:
https://deploy-preview-8037--kongdocs.netlify.app/gateway/2.7.x/
https://deploy-preview-8037--kongdocs.netlify.app/gateway/2.6.x/
https://deploy-preview-8037--kongdocs.netlify.app/gateway/changelog/

Checklist

• Review label added
• Conditional version tags added, if applicable.

[netlify]

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[github-actions]

⚠️ This PR edits generated files. Please make sure that the source file is updated.

https:/Kong/kong/blob/master/UPGRADE.md:

• app/gateway/2.6.x/install-and-run/upgrade-oss.md
• app/gateway/2.7.x/install-and-run/upgrade-oss.md

---

https:/Kong/kong/tree/master/kong/pdk:

• app/gateway/2.6.x/pdk/index.md
• app/gateway/2.6.x/pdk/kong.client.md
• app/gateway/2.6.x/pdk/kong.client.tls.md
• app/gateway/2.6.x/pdk/kong.cluster.md
• app/gateway/2.6.x/pdk/kong.ctx.md
• app/gateway/2.6.x/pdk/kong.ip.md
• app/gateway/2.6.x/pdk/kong.log.md
• app/gateway/2.6.x/pdk/kong.nginx.md
• app/gateway/2.6.x/pdk/kong.node.md
• app/gateway/2.6.x/pdk/kong.request.md
• app/gateway/2.6.x/pdk/kong.response.md
• app/gateway/2.6.x/pdk/kong.router.md
• app/gateway/2.6.x/pdk/kong.service.md
• app/gateway/2.6.x/pdk/kong.service.request.md
• app/gateway/2.6.x/pdk/kong.service.response.md
• app/gateway/2.6.x/pdk/kong.table.md
• app/gateway/2.7.x/pdk/index.md
• app/gateway/2.7.x/pdk/kong.client.md
• app/gateway/2.7.x/pdk/kong.client.tls.md
• app/gateway/2.7.x/pdk/kong.cluster.md
• app/gateway/2.7.x/pdk/kong.ctx.md
• app/gateway/2.7.x/pdk/kong.ip.md
• app/gateway/2.7.x/pdk/kong.log.md
• app/gateway/2.7.x/pdk/kong.nginx.md
• app/gateway/2.7.x/pdk/kong.node.md
• app/gateway/2.7.x/pdk/kong.request.md
• app/gateway/2.7.x/pdk/kong.response.md
• app/gateway/2.7.x/pdk/kong.router.md
• app/gateway/2.7.x/pdk/kong.service.md
• app/gateway/2.7.x/pdk/kong.service.request.md
• app/gateway/2.7.x/pdk/kong.service.response.md
• app/gateway/2.7.x/pdk/kong.table.md

---

https:/Kong/kong/tree/master/autodoc/cli:

• app/gateway/2.6.x/reference/cli.md
• app/gateway/2.7.x/reference/cli.md

---

https:/Kong/kong-ee/edit/master/kong.conf.default:

• app/gateway/2.6.x/reference/configuration.md
• app/gateway/2.7.x/reference/configuration.md