Add TimescaleDB PostgreSQL extension

[shusaan]

This PR adds support for the timescaledb extension to the postgres-extensions-containers project.

Closes #58

Changes

• Added timescaledb directory with Dockerfile and metadata.hcl
• Updated CI/CD workflows to include timescaledb in the build pipeline

[shusaan]

Hi @NiccoloFei Please check this PR when you get a chance. Thank You

[phippg]

As I was looking into adding the timescaledb-toolkit extension today I was wondering if there might be a licensing problem as this PR currently stands.

TimescaleDB is licensing parts of the source (and compiled binaries) differently, namely Apache 2.0 and the Tiger Data License (TSL) (see here). The Debian packages used here are partially TSL-licensed, which I'm assuming conflicts with the CNCF License Allowlist requirement.

Licensing and IP ownership: the extension's licensing must be compatible with the project's goals. We approve all licences that are on the CNCF Allowed Third-Party Licence Policy list (see CNCF Allowed Licence Policy).

[shusaan]

@phippg Thanks for catching this! You're right about the TSL compatibility problem. btw I am waiting for this PR. after that will open PR for timescaleDB_toolkit

we need to build from source using APACHE_ONLY=1 to include only Apache 2.0 licensed features and exclude TSL components. This would give us a limited but fully CNCF-compliant TimescaleDB build.

Is this approach acceptable, or would you prefer a different solution?
@gbartolini @NiccoloFei

[phippg]

I think you don't necessarily need to build from source, there are Debian packages that include only the open source parts of TimescaleDB (e.g. https://packagecloud.io/timescale/timescaledb/packages/debian/trixie/timescaledb-2-oss-postgresql-18_2.24.0~debian13-1801_amd64.deb?distro_version_id=221). The listed files don't include any timescaledb-tsl-*.so binaries.

According to the TimescaleDB Toolkit repository it is fully TSL-licensed unfortunately. If the CNCF license requirements are set in stone for the addition of extension images to this repository, I won't be able to use ones for TimescaleDB (but I do understand that there are valid reasons for them).