BUG: Unclear error message when merging tables and passing invalid option to validate

[raisadz]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

import pandas as pd
df1 = pd.DataFrame({'a': [1,2,3]})
df2 = pd.DataFrame({'a': [2,3,3]})
df1.merge(df2, on='a', validate='one_to_1')

"ValueError: Not a valid argument for validate"

Issue Description

Unclear error message. The error message with a list of the valid arguments would be useful.

Expected Behavior

"ValueError: "one_to_1" is not a valid argument. Valid arguments are:

• "1:1"
• "1:m"
• "m:1"
• "m:m"
• "one_to_one"
• "one_to_many"
• "many_to_one"
• "many_to_many""

I will create a pull request to change the error message if that's fine.

Installed Versions

INSTALLED VERSIONS

commit : 3872572
python : 3.8.13.final.0
python-bits : 64
OS : Linux
OS-release : 5.10.16.3-microsoft-standard-WSL2
Version : #1 SMP Fri Apr 2 22:23:49 UTC 2021
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : C.UTF-8
LOCALE : en_US.UTF-8

pandas : 2.0.0.dev0+499.g3872572512.dirty
numpy : 1.23.4
pytz : 2022.5
dateutil : 2.8.2
setuptools : 65.5.0
pip : 22.3
Cython : 0.29.32
pytest : 7.2.0
hypothesis : 6.56.4
sphinx : 4.5.0
blosc : None
feather : None
xlsxwriter : 3.0.3
lxml.etree : 4.9.1
html5lib : 1.1
pymysql : 1.0.2
psycopg2 : 2.9.3
jinja2 : 3.0.3
IPython : 8.6.0
pandas_datareader: 0.10.0
bs4 : 4.11.1
bottleneck : 1.3.5
brotli :
fastparquet : 0.8.3
fsspec : 2021.11.0
gcsfs : 2021.11.0
matplotlib : 3.6.1
numba : 0.56.3
numexpr : 2.8.3
odfpy : None
openpyxl : 3.0.10
pandas_gbq : 0.17.9
pyarrow : 9.0.0
pyreadstat : 1.2.0
pyxlsb : 1.0.10
s3fs : 2021.11.0
scipy : 1.9.3
snappy :
sqlalchemy : 1.4.42
tables : 3.7.0
tabulate : 0.9.0
xarray : 2022.10.0
xlrd : 2.0.1
zstandard : 0.18.0
tzdata : None