Consolidate JWT implementation

What does this MR do and why?

There are similarities and the code duplications between Gitlab::Ci::Jwt, Gitlab::Ci::JwtV2 and GoogleCloud::Jwt.
This MR introduces new classes Authn::JSONWebToken::ProjectTokenClaims and Gitlab::CI::JwtBase and refactors existing classes.

The following diagram reflects the changes:

graph TD;
    JSONWebToken::RSAToken --> Gitlab::Ci::JwtBase
    JSONWebToken::Token --> Gitlab::Ci::JwtBase
    Gitlab::Ci::JwtBase --> GoogleCloud::Jwt
    Gitlab::Ci::JwtBase --> Gitlab::Ci::Jwt
    Authn::JSONWebToken::ProjectTokenClaims --> GoogleCloud::Jwt
    Authn::JSONWebToken::ProjectTokenClaims --> Gitlab::Ci::Jwt
    Gitlab::Ci::Jwt --> Gitlab::Ci::JwtV2

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

No.

How to set up and validate locally

The changes in GoogleCloud::Jwt

1. Required setup for Google Cloud is described here

2. Prepare the project with the Google Artifact Management and Google Cloud IAM integrations.

3. Visit http://gdk.test:3000/-/graphql-explorer and create the request.

   query getGarArtifactsFromProject {
     project(fullPath: "<project full path>") {
       googleCloudArtifactRegistryRepository {
         projectId,
         repository,
         artifactRegistryRepositoryUrl,
         artifacts {
           nodes {
             ... on GoogleCloudArtifactRegistryDockerImage {
               name
             }
           }
         }
       }
     }
   }

   The request should return all requested data and doesn't contain any errors. The successful response means the correct token exchange using JWT token with the glgo service.

The changes in Gitlab::Ci::Jwt, Gitlab::Ci::JwtV2

I'm relying on the tests suite that does encoding/decoding and asserts all required fields.

Related to #435739 (closed)