Mark looker_sdk as an optional dependency

[sfc-gh-cnivera]

Some users may not want to run through partner flows, in which case installing the Looker SDK is unnecessary. Following the discussion in #150 (comment), this PR moves looker-sdk into the "extra" dependencies section, meaning it won't be installed unless specified (e.g. poetry install -E looker).

To support this, I made some small refactors to only import looker conditionally. The popup will now be triggered if the user attempts to click the "Start with partner semantic model" button.

Shown below is a video showing that without looker installed, the rest of the app is functional, and a warning pops up if a user attempts to use the Looker integration without the SDK.

CleanShot.2024-09-10.at.14.30.06.mp4

[sfc-gh-twhite]

This LGTM! Awesome job, I tested this extra install using pip and all seems to work well.

One non-blocking note - should we add a small block to the README to indicate that if a user wishes to leverage Looker (insert fancy words as to why one would want to use this solution with Looker)?

Note

To use the Looker features, you will need to install the extra.
pip install -e ".[looker]"

[sfc-gh-jsummer]

@sfc-gh-twhite - To your point about adding a note for install, we should have a partner semantic tool section in the updated README that contains such information and instructions. I can write when we are ready.

[sfc-gh-cnivera]

Good call @sfc-gh-twhite, stubbed out a small section with those instructions! We can definitely flesh out this section in a subsequent PR @sfc-gh-jsummer.