DDL SQL expressions

[nils-braun]

This PR introduces four new SQL expressions, which are added to the Apache Calcite parser and also understood by dask-sql.
They are:

-- show all schemas (currently only "schema")
SHOW SCHEMAS

-- show all registered tables
SHOW TABLES FROM "schema"

-- show all columns and column types for a table
SHOW COLUMNS FROM "table"

-- create a new dask dataframe and register it directly at the context
-- by calling one of the dd.read_* functions
-- with the given additional parameters.
CREATE TABLE "df" WITH (
  location = '/some/path',
  format = 'csv',
  ...
)

• Currently I needed to copy all "reservedKeywords" into the parser config. I guess there should be a better way to do this, but I will need to find out how. -> Fixed by bumping the calcite dependency version to 1.26 (where exactly this is implemented with a default file)

[codecov-io]

Codecov Report

Merging #55 into main will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             main       #55      +/-   ##
===========================================
+ Coverage   99.89%   100.00%   +0.10%     
===========================================
  Files          24        29       +5     
  Lines         992      1091      +99     
  Branches      142       153      +11     
===========================================
+ Hits          991      1091     +100     
+ Misses          1         0       -1     

Impacted Files	Coverage Δ
dask_sql/mappings.py	100.00% <ø> (ø)
dask_sql/context.py	100.00% <100.00%> (+1.06%)	⬆️
dask_sql/physical/rel/custom/__init__.py	100.00% <100.00%> (ø)
dask_sql/physical/rel/custom/columns.py	100.00% <100.00%> (ø)
dask_sql/physical/rel/custom/create.py	100.00% <100.00%> (ø)
dask_sql/physical/rel/custom/schemas.py	100.00% <100.00%> (ø)
dask_sql/physical/rel/custom/tables.py	100.00% <100.00%> (ø)
dask_sql/physical/rel/logical/project.py	100.00% <100.00%> (ø)
dask_sql/physical/rel/logical/table_scan.py	100.00% <100.00%> (ø)
... and 4 more

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