Publish v2.1.5 (#284)

Release new versions of legacy python client (#286)

Includes deprecation notice added in
#285

New versions available at:
* https://pypi.org/project/datacommons/1.4.4/
* https://pypi.org/project/datacommons-pandas/0.0.4/

Release new versions of legacy python client (#286)

Includes deprecation notice added in
#285

New versions available at:
* https://pypi.org/project/datacommons/1.4.4/
* https://pypi.org/project/datacommons-pandas/0.0.4/

Publish v2.1.4 (#282)

Bump version to v2.1.3 (#279)

Updates changelog and version

Pass a header into calls to mixer for usage logs (#276)

- Adds a `clientlib-python` header to the newer `datacommons_client`
client library
- This does not include the older `datacommons` client because it makes
calls to the V1 API, which will be deprecated soon.
- These are used in Mixer's usage logs
- The header accepts an optional `surface_header_value` tag in the
observation endpoints so that other DC surfaces that make calls to the
client library (MCP server, DataGemma, etc.) can be tracked.
- Theoretically, others could also pass in other values for this tag if
they make calls directly to the python client library. Like with custom
DCs, I plan to accept that this might happen in rare cases because these
usage logs will be aggregated over many queries.

Tests:
- Checked with local mixer that the metadata is correctly updated in the
`clientlib-python` case and when we pass in `metadata_source`
- Modified current test suite to include this header in the expected
response.

v2.1.1 (#270)

Test version:
[test.pypi.org/project/datacommons-client/2.1.1](https://test.pypi.org/project/datacommons-client/2.1.1/)

v2.1.0 (#254)

Test version: https://test.pypi.org/project/datacommons-client/2.1.0rc1/

`v2.0.0` (#236)

Version bumped to `v2.0.0`.

Release py1.4.3 and pd0.0.3 for returning empty data structures inste…

…ad of erroring on no data. (#166)