Add changelog entry for new documenteer CLI

changelog.d/20231212_141904_jsick_DM_42023.md

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+### New features
+
+- New command-line interface for technote authors.
+
+  - `documenteer technote migrate` automates to the process of migrating an old technote to the new format.
+  - `documenteer technote add-author` adds an author to a technote's `technote.toml` file using data from the `authordb.yaml` file in https://github.com/lsst/lsst-texmf.
+  - `documenteer technote sync-authors` refreshing author information in a `technote.toml` file with information from the `authordb.yaml` file. This requires that individual authors have `internal_id` fields to correlate with `authordb.yaml`.