feat: Add PKI capability

[snocorp]

Description

Add the ability to generate PKI certificates from Vault's PKI engine. You can now use the pki option to generate a certificate and private key for a given role.

with:
    pki: |
        pki/issue/rolename {"common_name": "role.mydomain.com", "ttl": "1h"} ;
        pki/issue/otherrole {"common_name": "otherrole.mydomain.com", "ttl": "1h"} ;
```

Resulting in:

```bash
ROLENAME_CA=-----BEGIN CERTIFICATE-----...
ROLENAME_CERT=-----BEGIN CERTIFICATE-----...
ROLENAME_KEY=-----BEGIN RSA PRIVATE KEY-----...
ROLENAME_CA_CHAIN=-----BEGIN CERTIFICATE-----...
OTHERROLE_CA=-----BEGIN CERTIFICATE-----...
OTHERROLE_CERT=-----BEGIN CERTIFICATE-----...
OTHERROLE_KEY=-----BEGIN RSA PRIVATE KEY-----...
OTHERROLE_CA_CHAIN=-----BEGIN CERTIFICATE-----...

Checklist

• Added CHANGELOG entry (only for user-facing changes)

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[kpcraig]

Hey @snocorp, apologies for the silence on this, and thanks for the contribution. I know we were a bit worried about breaking the restriction on GET only calls, but given that the call here is about retrieving credentials and not about changing Vault's config, it should be fine.

I'll give the code a look over and hopefully we can get this in sooner rather than later!

[kpcraig]

LGTM!

[snocorp]

@kpcraig Thanks so much for reviewing and merging! I noticed the build is failing after merging and I believe we need to update the docker compose command. I've created #567 to address this.

[fairclothjm]

@kpcraig Thanks for reviewing this one. I don't see the related changes to dist/index.js in this PR so we will need to make sure to make that change before we do the release.

[snocorp]

@fairclothjm Thanks, I didn't realize that was part of the PR process but in retrospect it makes sense. Would it be helpful if I created a new PR for that? I'd love to get a new release so we can start to use it internally.

[snocorp]

@kpcraig @fairclothjm I've created #568 to update the build output in case that helps to get the next release out.