feat(gateway): Solace Log plugin

[lena-larionova]

Description

Fixes #2621

Document new Solace Log plugin.

Preview Links

https://deploy-preview-2730--kongdeveloper.netlify.app/plugins/solace-log/

Checklist

• Tested how-to docs. If not, note why here.
• All pages contain metadata.
• Any new docs link to existing docs.
• All autogenerated instructions render correctly (API, decK, Konnect, Kong Manager).
• Style guide (capitalized gateway entities, placeholder URLs) implemented correctly.
• Every page has a description entry in frontmatter.
• Add new pages to the product documentation index (if applicable).

[netlify]

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[outsinre]

LGTM unless the "broken links" error in the CI.

[lena-larionova]

LGTM unless the "broken links" error in the CI.

The broken links are both false positives:

• https://deploy-preview-2730--kongdeveloper.netlify.app/plugins/solace-consume/ - plugin is being added in Feat(gateway): Solace Consume plugin #2768, link will be resolved when both are merged
• https://deploy-preview-2730--kongdeveloper.netlify.app/plugins/solace-log/unreleased/reference/#schema--config-message-custom-fields-by-lua - doesn't exist, but link checker was picking up an older version of the build. The new (working) link is https://deploy-preview-2730--kongdeveloper.netlify.app/plugins/solace-log/reference/#schema--config-message-custom-fields-by-lua

[cloudjumpercat]

LGTM!