Automated publish

Co-authored-by: Buildkite <buildkite@sourcegraph.com>

Automated publish

Co-authored-by: Buildkite <buildkite@sourcegraph.com>

Automated publish

Co-authored-by: Buildkite <buildkite@sourcegraph.com>

Automated publish

Co-authored-by: Buildkite <buildkite@sourcegraph.com>

Automated publish

Co-authored-by: Buildkite <buildkite@sourcegraph.com>

Sunset notice for k3s and AMI deployment type in repo docs

This repo and the AMI/k3s deployment methods were sunset in Sourcegraph
7.0.0 (#200 added the sunset notice; Sourcegraph is now on 8.x).

Replaces the README's stale content (instance size chart, AMI details,
link to a docs page that no longer exists) with a short deprecation
notice and a link to the current [Deployment
Overview](https://sourcegraph.com/docs/self-hosted/deploy), which covers
Sourcegraph Cloud, Kubernetes Helm, and Docker Compose.

Co-authored-by: Amp <amp@ampcode.com>

Pins every GitHub Action referenced by a tag or branch in this
repository's workflows to the full commit SHA that ref currently
resolves to, so behavior is unchanged. The resolved version is kept as a
trailing comment for readability and for Dependabot/Renovate updates.

This follows GitHub's recommendation to [pin versions of
actions](https://learn.github.com/well-architected/application-security/recommendations/actions-security#pin-versions-of-actions)
to a full-length commit SHA.

| File | Action | Previous ref | Pinned SHA (version) |
| --- | --- | --- | --- |
| `.github/workflows/backport.yml` | `sourcegraph/backport` | `v2` |
`014323f95529941f87ccc021caae11e095521f36` (v2.0.12) |

[_Created by a Sourcegraph agentic batch
change._](https://sourcegraph.sourcegraph.com/batch-change-agents/1257)