docs: add CodeCommit SSH key instructions

Signed-off-by: Zakhar Dvurechensky <72825626+Zakharden@users.noreply.github.com>

Author: Zakharden

content/en/flux/installation/bootstrap/aws-codecommit.md

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+---
+title: Flux bootstrap for AWS CodeCommit
+linkTitle: AWS CodeCommit
+description: "How to bootstrap Flux with AWS CodeCommit"
+weight: 50
+---
+
+To install Flux on an EKS cluster using a CodeCommit repository as the source of truth,
+you can use the [`flux bootstrap git`](generic-git-server.md) command.
+
+{{% alert color="danger" title="Required permissions" %}}
+To bootstrap Flux, the person running the command must have **cluster admin rights** for the target Kubernetes cluster.
+It is also required that the person running the command has **pull and push rights** for the CodeCommit repository.
+{{% /alert %}}
+
+## Bootstrap over SSH
+
+{{% alert color="info" title="Private VPC" %}}
+If your VPC is configured without internet access, or if you prefer that the access is over a private connection,
+you need to set up a VPC endpoint to access CodeCommit by following the
+guide [Using AWS CodeCommit with interface VPC endpoints](https://docs.aws.amazon.com/codecommit/latest/userguide/codecommit-and-interface-VPC.html).
+{{% /alert %}}
+
+Create a CodeCommit repository and generate a PEM-encoded RSA SSH private key
+with a passphrase:
+
+```sh
+ssh-keygen -t rsa -b 4096 -m PEM -f ./codecommit_rsa
+```
+
+Upload the SSH public key to the IAM user that Flux will use to access
+CodeCommit:
+
+```sh
+aws iam upload-ssh-public-key \
+  --user-name codecommit-user \
+  --ssh-public-key-body file://codecommit_rsa.pub
+```
+
+The output will contain a field called `SSHPublicKeyID`:
+
+```json
+{
+    "SSHPublicKey": {
+        "SSHPublicKeyId": "<SSH-Key-ID>",
+        "Fingerprint": "<fingerprint>",
+        "SSHPublicKeyBody": "<public-key>",
+        "Status": "Active",
+        "UploadDate": "<timestamp>"
+    }
+}
+```
+
+Run bootstrap using the `SSHPublicKeyId` as the SSH username:
+
+```sh
+flux bootstrap git \
+  --url=ssh://<SSHPublicKeyId>@git-codecommit.<region>.amazonaws.com/v1/repos/<repository> \
+  --branch=<my-branch> \
+  --private-key-file=./codecommit_rsa \
+  --password=<key-passphrase> \
+  --path=clusters/my-cluster
+```
+
+Do not use the IAM user name as the SSH username in the repository URL.
+CodeCommit expects the SSH key ID assigned to the uploaded public key.
+
+You can also pipe the passphrase e.g. `echo key-passphrase | flux bootstrap git`.
+
+The SSH private key and the known hosts keys are stored in the cluster as a Kubernetes
+secret named `flux-system` inside the `flux-system` namespace.
+
+For the full CodeCommit SSH setup, including where to find the SSH Key ID, see
+the AWS CodeCommit SSH documentation for
+[Linux, macOS, or Unix](https://docs.aws.amazon.com/codecommit/latest/userguide/setting-up-ssh-unixes.html)
+and [Windows](https://docs.aws.amazon.com/codecommit/latest/userguide/setting-up-ssh-windows.html).
+
+{{% alert color="info" title="SSH Key rotation" %}}
+To rotate the SSH key, delete the `flux-system` secret from the cluster and re-run
+the bootstrap command using a new PEM-encoded RSA SSH private key.
+{{% /alert %}}