Prepare Changelog for Automation (#7309)

This PR prepares the changelog to be automatically updated during releases.

Authors:
  - GALI PREM SAGAR (@galipremsagar)

Approvers:
  - Keith Kraus (@kkraus14)
  - AJ Schmidt (@ajschmidt8)

URL: #7309

CHANGELOG.md

@@ -1,40 +1,3 @@
-# cuDF 0.18.0 (Date TBD)
-
-## New Features
-- PR #6856 Add groupby idxmin, idxmax aggregation
-- PR #6847 Add a cmake find module for cuFile in JNI code
-- PR #6902 Implement `DataFrame.quantile` for `datetime` and `timedelta` data types
-- PR #6814 Implement `cudf::reduce` for `decimal32` and `decimal64` (part 1)
-- PR #6929 Add `Index.set_names` api
-- PR #6907 Add `replace_null` API with `replace_policy` parameter, `fixed_width` column support
-- PR #6885 Share `factorize` implementation with Index and cudf module
-- PR #6775 Implement cudf.DateOffset for months
-- PR #7069 Pack/unpack for serialization/deserialization of table_views
-- PR #7039 Support contains() on lists of primitives
-
-## Improvements
-
-- PR #6938 Pass numeric scalars of the same dtype through numeric binops
-- PR #6275 Update to official libcu++ on Github
-- PR #6838 Fix `columns` & `index` handling in dataframe constructor
-- PR #6750 Remove **kwargs from string/categorical methods
-- PR #6585 Add dictionary support to libcudf groupby functions
-- PR #6909 Support reading byte array backed decimal columns from parquet files
-- PR #6939 Use simplified `rmm::exec_policy`
-- PR #6512 Refactor rolling.cu to reduce compile time
-- PR #6982 Disable some pragma unroll statements in thrust `sort.h`
-- PR #7051 Verify decimal cast in java package
-- PR #7120 Verify window operations on decimal in java package
-
-## Bug Fixes
-
-- PR #6884 Correct the sampling range when sampling with replacement
-- PR #6903 Add null count test for apply_boolean_mask
-- PR #6922 Fix N/A detection for empty fields in CSV reader
-- PR #6912 Fix rmm_mode=managed parameter for gtests
-- PR #6943 Fix join with nulls not equal performance
-- PR #6945 Fix groupby agg/apply behaviour when no key columns are provided 
-- PR #6942 Fix cudf::merge gtest for dictionary columns
 # 0.18.0
 
 Please see https://github.com/rapidsai/cudf/releases/tag/branch-0.18-latest for the latest changes to this development branch.