docs: connectors

[snkas]

Improves the connectors documentation:

• General connectors index
• Input connectors
• Output connectors

Is this a user-visible change (yes/no): yes

[lalithsuresh]

@snkas This is a great start! Thanks for working on this. Main suggestions (you can also do these over multiple PRs):

• More examples for specific workflows people are trying to accomplish would be nice. I like the "from curl" and "from python" examples (which shows, given a connector json object, how you'd apply it). Perhaps also show several examples of connector json objects for common needs (e.g., Kafka without authentication, Kafka with SSL, Kafka when connecting to Confluent, Kafka with certificates etc). The HTTP connector also has several examples you could show.
• Do a language revision to prefer active voice over passive voice.

[ryzhyk]

Great stuff, thanks, @snkas !