refactor(jenkins-plugins): convert to class-based datasource

[JamieMagee]

Changes:

• Converts jenkins-plugins datasource to be class-based
• Switches to using Renovate's standard caching instead of custom internal caching

Context:

#8647

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please tick one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[JamieMagee]

I will create and run this on a test repo before merging.

[rarkins]

LGTM once tested

[viceice]

just some small things 🙃

[JamieMagee]

Run on https://github.com/renovate-reproductions/12702. Created 4 PRs:

• Update dependency apache-httpcomponents-client-4-api to v4.5.10-2.0 renovate-reproductions/12702#1
• Update dependency authentication-tokens to v1.4 renovate-reproductions/12702#2
• Update dependency blueocean to v1.25.1 renovate-reproductions/12702#3
• Update dependency email-ext to v2 renovate-reproductions/12702#4

Only made 2 requests to Jenkins API

"hostStats": {
  "api.github.com": {"requestCount": 26, "requestAvgMs": 213, "queueAvgMs": 0},
  "updates.jenkins.io": {
    "requestCount": 2,
    "requestAvgMs": 3688,
    "queueAvgMs": 1
  }
}

Followup run made 0 requests to Jenkins API (AKA only used cache)

"hostStats": {"api.github.com": {"requestCount": 17, "requestAvgMs": 451, "queueAvgMs": 0}}

[renovate-release]

🎉 This PR is included in version 29.13.5 🎉

The release is available on:

• GitHub release
• 29.13.5

Your semantic-release bot 📦🚀