Component: Add input for etcd key or prefix watcher

[gregfurman]

Changes

• Create new etcd Watch input, that will watch for new PUT or DELETE operations on a specific key or prefix (see Watch API docs).
• Add integration tests for watching a single key and all keys for changes.
• Include extensive configuration options for watch stream operations.
• Updated website with new docs.

TODO

• Determine version this will be released in -- currently set as 1.x.x
• Include a better description for the etcd component
• Improve the leasing capabilities
• Create an output sink for operating on etcd (i.e PUTs, DELETEs, new lease creation)

[jem-davies]

some changes required I think

[danriedl]

hey just checking in,
to let you know i created a PR for etcd cache/input in the old benthos-dev/benthos project in april:
redpanda-data/connect#2555

[gregfurman]

Hey @danriedl! Wow that looks awesome. Since you have context on etcd, Go, and delcarative pipelines, would love it if you gave these changes a look? Else, if you want to try combine our solutions I think that'd be awesome.

Happy to chat on Discord or Slack too :)