feat: SQL commands to show sources and connectors

[xx01cyx]

After #7110 and #7281, we should support showing all connectors (and maybe showing all sources as well).

Two solutions for this:

1. • Support SHOW SOURCES to show all sources created by CREATE SOURCE. Do not include those created by CREATE TABLE WITH (connector = 'xxx').
   • Support SHOW CONNECTORS to show all connectors created by both CREATE SOURCE and CREATE TABLE WITH (connector = 'xxx').

2. Only support SHOW SOURCES to show all connectors created by both CREATE SOURCE and CREATE TABLE WITH (connector = 'xxx').

[xx01cyx]

cc. @st1page @yezizp2012 @fuyufjh

[tabVersion]

upvote for solution 1.

connector should be seen as a component inside a source or table. If a connector is created within a table, it can not be seen as a source.

[fuyufjh]

I concur with @tabVersion

[hzxa21]

Since MATERIALIZED SOURCE has been changed to source TABLE, I think we should also show it in show tables and information_schema.tables (See #7739 )

[neverchanje]

So far we've supported a bunch of ways for displaying the tables and sources:

• show sources
• show tables
• rw_tables
• rw_sources

There is no need to add more. Let's close the issue.