[doc] Added docs for Debezium DB2 connector

[devinbost]

Docs for PR devinbost/pulsar#15
and apache/pulsar#19821

• doc
• doc-required
• doc-not-needed
• doc-complete

[github-actions]

@devinbost Please add the following content to your PR description and select a checkbox:

- [ ] `doc` <!-- Your PR contains doc changes -->
- [ ] `doc-required` <!-- Your PR changes impact docs and you will update later -->
- [ ] `doc-not-needed` <!-- Your PR changes do not impact docs -->
- [ ] `doc-complete` <!-- Docs have been already added -->

[tisonkun]

Convert to Draft to prevent accidentally merging before we get the function PR merged.

[lhotari]

Closing since DB2 connector isn't part of Pulsar