programmatically list supported dialects

[reata]

Is your feature request related to a problem? Please describe.
Since the introduction of sqlfluff as parser implementation in sqllineage v1.4.x, it evolves a lot and particularly three new dialects (duckdb, greenplum, trino) were introduced after sqllineage v1.4.0 release. Although we can pass these three new dialects to sqllineage but they're not listed explicitly when calling sqllineage --dialects, nor do they show up in frontend select.

Describe the solution you'd like
We should programmatically list supported dialects, so later when we upgrade sqlfluff to newer version, the newly added dialect are automatically added