Pki settings extension

[mgsharm]

Issue number:

Closes #3657

Description of changes:

• Creates pki settings extension and uses it in every variant's settings model.
• Creates settings-pki RPM package that installs the extension binary.

Testing done:

• Built aws-dev variant with the settings-pki installed. Launched ec2 instance with the aws-dev variant ami. Connected with the instance via SSM to run apiclient commands.
• Called apiclient to verify the settings-pki worked as expected.

[ssm-user@control]$ apiclient set pki.my-trusted-bundle.data="LS0tLS1..." \
> pki.my-trusted-bundle.trusted=true

[ssm-user@control]$ apiclient get settings.pki
{  
   "settings":  {
       "pki": {      
           "my-trusted-bundle": {       
                "data": "LS0tLS1...",
                 "trusted": true
            }
       }
   }
}

• Also tested by building locally.

> cert_content=$(cat test-pem)
> json_value="{\"foo\":{\"data\":\"$cert_content\",\"trusted\":true}}"
> cargo run proto1 set --setting-version v1 --value "$json_value"
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.24s
     Running `/home/fedora/bottlerocket/sources/target/debug/settings-extension-pki proto1 set --setting-version v1 --value '{"foo":{"data":"LS0tLS1...,"trusted":true}}'`

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.