Configurable server_settings

[drnextgis]

In certain scenarios, it would be beneficial to provide a method for setting runtime parameters, such as statement_timeout. Presently, stac-fastapi-pgstac does not include this functionality. This pull request introduces the capability to configure these parameters using environment variables. Example (test.py):

import asyncio
import asyncpg

from stac_fastapi.types.config import ApiSettings
from pydantic import BaseModel, Extra


class ServerSettings(BaseModel, extra=Extra.allow):
   search_path: str = "pgstac,public"
   application_name: str = "pgstac"


class Settings(ApiSettings):
    postgres_user: str
    postgres_pass: str
    server_settings: ServerSettings = ServerSettings()

    class Config(ApiSettings.Config):
       env_nested_delimiter = "__"


async def main():
    settings = Settings()
    connection_string = f"postgres://{settings.postgres_user}:{settings.postgres_pass}@localhost:5439/postgis"
    pool = await asyncpg.create_pool(
        connection_string,
        server_settings=settings.server_settings.dict()
    )

    async with pool.acquire() as con:
        timeout = await con.fetch("SHOW statement_timeout")
        print(timeout)

    await pool.close()


asyncio.run(main())

$ POSTGRES_USER=username POSTGRES_PASS=password SERVER_SETTINGS__STATEMENT_TIMEOUT=42 python3 test.py
[<Record statement_timeout='42ms'>]

PR Checklist:

• pre-commit hooks pass locally
• Tests pass (run make test)
• Documentation has been updated to reflect changes, if applicable, and docs build successfully (run make docs)
• Changes are added to the CHANGELOG.

[drnextgis]

@vincentsarago thanks for taking the time to review the PR.

[jonhealy1]

@drnextgis @vincentsarago Is it worth putting a small section in the README explaining how this new functionality could be used?

[vincentsarago]

Is it worth putting a small section in the README explaining how this new functionality could be used?

@jonhealy1 let's not block this PR with this, but I think we should open an issue for updating the readme with the different environment variables that can be set to control the API