adapter: NebulaGraph

[wey-gu]

What are the key elements of this solution?

Add support of NebulaGraph

Why did you design your solution this way? Did you assess any alternatives? Are there tradeoffs?

n/a

Does this PR require a change to Harlequin's docs?

• No.
• Yes, and I have opened a PR at tconbeer/harlequin-web. feat: add NebulaGraph adapter harlequin-web#91
• Yes; I haven't opened a PR, but the gist of the change is: ...

Did you add or update tests for this change?

• Yes.
• No, I believe tests aren't necessary, adaptor tests are in https://github.com/wey-gu/harlequin-nebulagraph
• No, I need help with testing this change.

Please complete the following checklist:

• I have added an entry to CHANGELOG.md, under the [Unreleased] section heading. That entry references the issue closed by this PR.
• I acknowledge Harlequin's MIT license. I do not own my contribution.

[tconbeer]

A graph database! Cool! Thanks so much!