DOC: Add documentation for `groupby.ewm()` #22894

Job	Run time
Pyodide build	23m 9s
Linux-32-bit	18m 21s
Linux-Musl	15m 57s
macos-13 actions-310.yaml	43m 17s
macos-13 actions-311.yaml	43m 44s
macos-13 actions-312.yaml	47m 48s
macos-14 actions-310.yaml	19m 27s
macos-14 actions-311.yaml	18m 57s
macos-14 actions-312.yaml	18m 27s
windows-latest actions-311.yaml	1h 1m 14s
windows-latest actions-312.yaml	1h 5m 34s
windows-latest actions-310.yaml	58m 54s
python-freethreading	22m 36s
python-dev (macOS-13)	25m 35s
python-dev (macOS-14)	11m 25s
python-dev (ubuntu-22.04)	20m 13s
python-dev (windows-latest)	22m 13s
Locale: zh_CN	48m 55s
Future infer strings (without pyarrow)	1h 4m 29s
Minimum Versions	24m 56s
Downstream Compat	6m 37s
Numpy Dev	16m 57s
Locale: it_IT	48m 53s
Pyarrow Nightly	21m 15s
Future infer strings	1h 10m 0s
Pypy	1m 48s
ubuntu-22.04 actions-310.yaml	1h 11m 58s
ubuntu-22.04 actions-311.yaml	1h 8m 11s
ubuntu-22.04 actions-312.yaml	1h 8m 19s
ubuntu-24.04-arm actions-312.yaml	48m 30s
ubuntu-24.04-arm actions-311.yaml	49m 10s
ubuntu-24.04-arm actions-310.yaml	47m 45s
	19h 54m 34s

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