Add 0.22.0 release notes

Signed-off-by: Xavi Garcia <[email protected]>

docs/release-notes/s3gw-v0.22.0.md

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+# Release Notes - v0.22.0
+
+This release contains significant improvements and new bug fixes. Notably,
+this release brings improved multipart and sqlite stability.
+
+This release is meant for testing and feedback gathering. It is not recommended
+for production use.
+
+Should a bug be found and not expected to be related with known issues, one
+should feel encouraged to file an issue in our
+[Github repository](https://github.com/aquarist-labs/s3gw/issues/new/choose).
+
+## Features
+
+- rgw/sfs: Improved SQLite WAL usage
+- rgw/sfs: Improved disk usage when copying objects
+- rgw/sfs: Improved testing
+- ui: Various improvements
+
+## Fixes
+
+- rgw/sfs: Allow multiple delete markers
+- rgw/sfs: Fix various multipart transactions
+- rgw/sfs: Check number of file descriptors on start
+- rgw/sfs: Updated bucket stats
+- ui: unable to access UI due to admin ops verifying cert
+- ui: The Show/Hide button must have at least one default value
+- ui: Dropdown buttons are not rendered correct
+- ui: Disable caching of index.html
+
+## Breaking Changes
+
+## Known Issues