feat: Make pipeline required on connect

[raulb]

Description of change

Fixes https://github.com/meroxa/product/issues/128

Continuation of #189.

It also updates the wording to make it more specific when creating a connector within the context of a pipeline.

Type of change

• New feature
• Bug fix
• Refactor
• Documentation

How was this tested?

• Unit Tests
• Tested in staging

Demo

Before this pull-request

$ meroxa connect --input my-resource.Table --config '{"key":"value"}' --pipeline my-pipeline --source resource-1234 --destination resource-4567
Creating connector from source "resource-1234"...
Creating connector to destination "resource-4567"...
Source connector "connector-1234" and destination connector "connector-4567" successfully created!

After this pull-request

$ meroxa connect --input my-resource.Table --config '{"key":"value"}' --pipeline my-pipeline --source resource-1234 --destination resource-4567
Creating connector from source "resource-1234" in pipeline "my-pipeline"...
Creating connector to destination "resource-4567" in pipeline "my-pipeline"...
Source connector "connector-1234" and destination connector "connector-1234" successfully created!

Documentation updated

https://github.com/meroxa/meroxa-docs/pull/37