Add changelog entry for --concurrency flag

Co-authored-by: Isaac

Author: pietern

NEXT_CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * `databricks auth describe` now reports where U2M (`databricks-cli`) tokens are stored: `plaintext` (`~/.databricks/token-cache.json`) or `secure` (OS keyring), and the source of the choice (env var, config setting, or default).
 * Marked the default profile in the interactive pickers shown by `databricks auth switch`, `databricks auth logout`, `databricks auth token`, and `databricks auth login`, and moved it to the top of the list. `databricks auth login` and `databricks auth logout` now offer the same selectors as `databricks auth token` and `databricks auth switch` respectively.
+* Add `--concurrency` flag to `databricks sync` and `databricks bundle sync` to control the number of parallel requests to the workspace (default 20). Useful when uploading many medium-sized files where the previous fixed concurrency could trigger stream timeouts ([#5197](https://github.com/databricks/cli/pull/5197)).
 
 ### Bundles
 * Stop applying `presets.name_prefix` (and the dev-mode `[dev <user>]` rename) to `vector_search_endpoints` ([#5209](https://github.com/databricks/cli/pull/5209)).