Add pghydro (+ misc. extension desc. updates)

[EvanHStanton]

Add pghydro Dockerfile and Trunk.toml

• The files come pre-compiled, so no Makefile
• Similar to PostGIS, pghydro has other extensions bundled in the main GitHub repository (https://github.com/pghydro/pghydro)
• The other extensions depend on pghydro, and using Trunk ci workflow, the extension would build correctly, even with the output: Using extension_name: pghydro. However, installing consistently threw the following error:

Failed to fetch Trunk archive from v1 API: Found no Trunk project with name pghydro
error: Request to registry failed: No extension with the given name was found

• Therefore, this PR serves to publish only pghydro to Trunk, and not its companion extensions, by including the following in the Trunk.toml file:

    cd pghydro
    set -x
    mv pghydro* /usr/share/postgresql/15/extension
    """

[EvanHStanton]

Closing