[DSM] Add Data source icon

[kristenTian]

pending after UX provide the icon resource.

• update src/plugins/data_sources/server/saved_objects/data_source.ts icon
• update in index pattern

[KrooshalUX]

@kristenTian is this an icon for the "Saved Objects" table?

[zhongnansu]

@kristenTian is this still on track for 2.4?

[KrooshalUX]

In a decoupled world, which we are working towards, all connections will be a data source connection - therefore this icon may be added noise within the UI. @kgcreative wondering what your take is on this, and if we should design it, or design glyphs for different kinds of data sources (OpenSearch , AWS, Prometheus) or close this issue as not needed.

[kgcreative]

for document field types, we have icons for field types using (tokens). I can see a world where we have a "type" column that only uses an icon type as a token as well (would save space and help disambiguate). I think we need to explore this a bit more, since I could see [type icon] datasource.indexname -- my concern with this is if it would simply add extra potentially unnecessary visual noise.

[KrooshalUX]

(Was going to move this over but I dont have permissions) Closing this issue in favor of this one in the OUI repo: https://github.com/opensearch-project/oui/issues/313