Feature Request: Better way to look up current layer version

There's currently no clear way to find out the latest version of this Lambda layer. The documentation has to be manually updated (and is therefore likely to be incorrect), and then users need to find the right place in that documentation to see if a new version was published.

It would be good to have an automatically updated resource to fetch the latest version, e.g. a published URL on hashicorp.com, or a public SSM Parameter similar to [the instructions given by AWS for one of their extensions](https://docs.aws.amazon.com/systems-manager/latest/userguide/ps-integration-lambda-extensions.html#ps-integration-lambda-extensions-add).

The instructions in both the README and the hashicorp.com documentation could then point users to that, rather than referring to a specific version and going out of date.

----

For the x86 build, the README in this repo currently says to install version **25**:

```text
arn:aws:lambda::634166935893:layer:vault-lambda-extension:25
```

The [documentation on hashicorp.com](https://developer.hashicorp.com/vault/docs/deploy/aws/lambda-extension) still refers to version **18**:

```text
arn:aws:lambda::634166935893:layer:vault-lambda-extension:18
```

Using the AWS CLI, it looks like the latest version is actually **26**:

```text
aws lambda get-layer-version-by-arn --arn arn:aws:lambda:eu-west-1:634166935893:layer:vault-lambda-extension:25
...
"LayerArn": "arn:aws:lambda:eu-west-1:634166935893:layer:vault-lambda-extension",
"LayerVersionArn": "arn:aws:lambda:eu-west-1:634166935893:layer:vault-lambda-extension:25",
"Description": "Vault AWS Lambda Extension 0.13.2",
"CreatedDate": "2025-10-06T21:52:53.169+0000",
"Version": 25,
...
aws lambda get-layer-version-by-arn --arn arn:aws:lambda:eu-west-1:634166935893:layer:vault-lambda-extension:26
...
"LayerArn": "arn:aws:lambda:eu-west-1:634166935893:layer:vault-lambda-extension",
"LayerVersionArn": "arn:aws:lambda:eu-west-1:634166935893:layer:vault-lambda-extension:26",
"Description": "Vault AWS Lambda Extension 0.14.0",
"CreatedDate": "2026-03-10T15:43:20.661+0000",
"Version": 26,
```

Start with the README's Lambda layer installation instructions and compare them with the linked hashicorp.com documentation and AWS CLI output in the issue. Investigate how the published layer version can be exposed through an automatically updated public resource such as SSM, then update both documentation locations to use it; done means users can reliably discover the current version without manual version edits.

Written by the indexing model from the issue text.