Add level parameter to Triangle.drop()

[genedan]

Description

In the case of a Triangle with a multi-level index, level can be used to drop a specific level of the index via Triangle.drop().

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.

tri = cl.Triangle(
    data={
        'origin': [1985, 1985, 1985, 1986, 1986, 1987] * 4,
        'development': [1985, 1986, 1987, 1986, 1987, 1987] * 4,
        'paid': [300, 400, 500, 500, 600, 500] * 4,
        'company': ['ballstate', 'regressive'] * 12,
        'lob': (['auto'] * 6 + ['wkcomp'] * 6) * 2
    },
    origin='origin',
    development='development',
    columns=['paid'],
    index=['company', 'lob'],
    cumulative=True
)
print(tri.index)

      company     lob
0   ballstate    auto
1   ballstate  wkcomp
2  regressive    auto
3  regressive  wkcomp

print(tri.drop(index='wkcomp', level=1))

      company     lob
0   ballstate    auto
1  regressive    auto

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.