Don't show "Append Command" when onPartitionAppend prop is not provided

[mofojed]

Description

When the onPartitionAppend prop is not provided to IrisGrid, do not show the Append Command in the Partition selector, as it won't do anything.

Steps to reproduce

1. Open http://localhost:10000 and create a partition aware table:

from deephaven import new_table
from deephaven.column import int_col, double_col, string_col
grades1 = new_table([
    string_col("Name", ["Ashley", "Jeff", "Rita", "Zach"]),
    int_col("Test1", [92, 78, 87, 74]),
    int_col("Test2", [94, 88, 81, 70]),
    int_col("Average", [93, 83, 84, 72]),
    double_col("GPA", [3.9, 2.9, 3.0, 1.8])
])

grades2 = new_table([
    string_col("Name", ["Jose", "Martha", "Mary", "Richard"]),
    int_col("Test1", [67, 92, 87, 54]),
    int_col("Test2", [97, 99, 92, 63]),
    int_col("Average", [82, 96, 93, 59]),
    double_col("GPA", [4.0, 3.2, 3.6, 2.7])
])

from deephaven.parquet import write, read

write(grades1, "grades/school=elementary/part1.parquet")
write(grades2, "grades/school=middle/part2.parquet")

grades = read("grades")

This uses the format of Nested Parquet Tables to create a partition aware table.
2. Open the table in the iframe UI: http://localhost:10000/iframe/table?name=grades

Expected Results
2. "Append Command" button should not be there, as there is no console session to append the command to

Actual Results
2. "Append Command" button is there, and clicking it does nothing