[ENH] Support SQL "replace" function

[randerzander]

>>> from dask_sql import Context
>>> import pandas as pd

>>> c = Context()
>>> df = pd.DataFrame({"id": ["abc", "def", "bcd"]})
>>> c.create_table("df", df)
>>> c.sql("select replace(id, 'b', '') from df").compute()
Traceback (most recent call last):
  File "/opt/conda/envs/rapids/lib/python3.9/site-packages/dask_sql/physical/rex/core/call.py", line 1004, in convert
    operation = self.OPERATION_MAPPING[operator_name]
KeyError: 'replace'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/conda/envs/rapids/lib/python3.9/site-packages/dask_sql/physical/rex/core/call.py", line 1007, in convert
    operation = context.schema[schema_name].functions[operator_name]
KeyError: 'replace'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/conda/envs/rapids/lib/python3.9/site-packages/dask_sql/context.py", line 501, in sql
    return self._compute_table_from_rel(rel, return_futures)
  File "/opt/conda/envs/rapids/lib/python3.9/site-packages/dask_sql/context.py", line 830, in _compute_table_from_rel
    dc = RelConverter.convert(rel, context=self)
  File "/opt/conda/envs/rapids/lib/python3.9/site-packages/dask_sql/physical/rel/convert.py", line 61, in convert
    df = plugin_instance.convert(rel, context=context)
  File "/opt/conda/envs/rapids/lib/python3.9/site-packages/dask_sql/physical/rel/logical/project.py", line 57, in convert
    new_columns[random_name] = RexConverter.convert(
  File "/opt/conda/envs/rapids/lib/python3.9/site-packages/dask_sql/physical/rex/convert.py", line 73, in convert
    df = plugin_instance.convert(rel, rex, dc, context=context)
  File "/opt/conda/envs/rapids/lib/python3.9/site-packages/dask_sql/physical/rex/core/call.py", line 1009, in convert
    raise NotImplementedError(f"{operator_name} not (yet) implemented")
NotImplementedError: replace not (yet) implemented

Expected:

ac
def
cd