Supports field_ids during COPY TO

[aykut-bozkurt]

Adds field_ids option, which lets you specify how to assign field ids during COPY TO.
Supported values for it:

• none (default) => no field ids are written into parquet metadata.
• auto => pg_parquet generates fields ids starting from 0.
• <json string> => pg_parquet will use the given field ids. e.g.

create table test_table(a int, b text[]);
copy test_table to '/tmp/test.parquet' with (field_ids '{"a": 1, "b": {"__root_field_id": 2, "element": 3}}');

Closes #106.

[marcoslot]

Seems to work well, though I'm wondering whether we should throw an error for column names that cannot be found to prevent typos.

[marcoslot]

generally, it would be useful to add more comments to things as the code base is growing:

// implements parsing for the field_ids option in COPY .. TO statements

[codecov]

Codecov Report

Attention: Patch coverage is 70.39604% with 299 lines in your changes missing coverage. Please review.

Project coverage is 91.12%. Comparing base (f8c3d62) to head (cfa4dec).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pgrx_tests/copy_options.rs	63.01%	226 Missing ⚠️
src/arrow_parquet/schema_parser.rs	80.57%	34 Missing ⚠️
src/arrow_parquet/field_ids.rs	73.33%	28 Missing ⚠️
src/pgrx_tests/common.rs	73.68%	5 Missing ⚠️
src/parquet_copy_hook/copy_to_dest_receiver.rs	63.63%	4 Missing ⚠️
...c/parquet_copy_hook/copy_to_split_dest_receiver.rs	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
- Coverage   92.90%   91.12%   -1.79%     
==========================================
  Files          86       87       +1     
  Lines       11650    12479     +829     
==========================================
+ Hits        10823    11371     +548     
- Misses        827     1108     +281     

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