Add support for Kibana knowledge base entry assets

[pgayvallet]

What does this PR do?

Add support for Kibana knowledge base entries, as discussed in https://github.com/elastic/package-spec/issues/693

Knowledge base entries are a new Kibana type of content, living under kibana/knowledge_base_entry/*. A KB entry is composed of 3 parts:

• a manifest.yml file
• a fields folder, containing one or more fields file
• a content folder, containing one or more content file, containing the ES documents of the entry in an NDJSON format.

Please refer to the changes and the self-review for more details.

Why is it important?

As it is required for https://github.com/elastic/kibana/issues/192031 via https://github.com/elastic/kibana/issues/193849

Checklist

• [x] I have added test packages to test/packages that prove my change is effective.
• [x] I have added an entry in spec/changelog.yml.

Related issues

• Closes https://github.com/elastic/package-spec/issues/693
• Related to https://github.com/elastic/kibana/issues/193849

[elasticmachine]

:green_heart: Build Succeeded

• Buildkite Build
• Commit: cdb409846c86dc36eecb29a3c89591e50f632c40

History

• :green_heart: Build #829 succeeded 6dfa6776a0b0da2633b25522801cbb2640a8ef5d
• :green_heart: Build #828 succeeded 39fa4f88cc5b820a0118b5f798519971f443fba2
• :green_heart: Build #827 succeeded 748177009a3faad24353fcb8369e83cffba6a0bf
• :green_heart: Build #826 succeeded 05ebcadd9df303171fa200aeb2ea9d32672e9c99
• :green_heart: Build #824 succeeded 6ae9b3f2915c23a121f6c021efa94d457db6fd18
• :green_heart: Build #823 succeeded a9fea19da9027282571577fa674fdb7a0bfb4fc8

[jsoriano]

As a note related to this, the current issue in Kibana elastic/kibana#192484 will not considerate this new folder or subfolders (i.e. fields) when addign support for content packages @jsoriano @pgayvallet

No problem, Pierre already created an issue and started a PR for this:

• https://github.com/elastic/kibana/issues/193849
• https://github.com/elastic/kibana/pull/194209