chore: setup dependabot and GHA CI

[bajtos]

Based on https://github.com/filecoin-station/spark-stats/tree/main/.github,
with few tweaks to try out a better setup.

Links:

• Spark v2: DDO, Allocators, Data Quality Improvements space-meridian/roadmap#115
• Lightweight DDO Compatibility: Spark Piece Indexer space-meridian/roadmap#143

[bajtos]

@juliangruber hindsight please 🙏🏻

[juliangruber]

Out of curiosity, why did you go for a multiple workspaces layout here?

[juliangruber]

this limitation isn't necessary, as it prevents PRs targeting other branches from running CI

[bajtos]

Do you know why we have that limitation in spark-evaluate config?

https://github.com/filecoin-station/spark-evaluate/blob/f87560ec447d41ecaaadd3eafc7ab33d8eb2e078/.github/workflows/ci.yml#L5-L6

But not in spark-api config:

https://github.com/filecoin-station/spark-api/blob/0d79f8b060aac01d2f8c04d622aed3aded3dc707/.github/workflows/ci.yml#L5-L6

Git blame pointed me to this PR:

filecoin-station/spark-evaluate#198

[bajtos]

#8

[bajtos]

Out of curiosity, why did you go for a multiple workspaces layout here?

I should have explained that in the design doc.

Cross-posting #3 (comment):

Components:

• indexer: background service owning the persisted data, similar to spark-evaluate and spark-observer
• REST API server exposing that data - to be done later