[REFACTOR] Deprecate `development` in Triangle constructor

[henrydingliu]

Description

The development argument in the Triangle constructor is a misnomer. We are currently feeding in valuation

raa_df = pd.read_csv(
    "https://raw.githubusercontent.com/casact/chainladder-python/master/chainladder/utils/data/raa.csv"
)
raa = cl.Triangle(
    raa_df,
    origin="origin",
    development="development",
    columns="values",
    cumulative=True,
)
print(raa_df.head(10))

Is your feature request aligned with the scope of the package?

• Yes, absolutely!
• No, but it's still worth discussing.
• N/A (this request is not a codebase enhancement).

Describe the solution you'd like, or your current workaround.

1. introduce valuation as the equivalent of development
2. add age as an alternative
3. add deprecation notice to drop development from the constructor by 2.0

Do you have any additional supporting notes?

No response

Would you be willing to contribute this ticket?

• Yes, absolutely!
• Yes, but I would like some help.
• No.