[com.influxdata.telegraf] Add a few input plugins

[in-the-mood-for-mov]

Hi!

This is pull request that adds a few of the simpler input plugins for Telegraf.

• diskio
• kernel
• mem
• processes
• redis
• swap
• system

I'm on the fence about two things :

• Should I split this commit in multiple commits and/or PRs?
• I looked at the existing plugins, some were open modules and some were closed. I decided to open those that were non-trivial to let the user add configurations that could be out of sync. Maybe I should open all of them instead?

Thank you

[HT154]

Thanks! Just one issue in the redis input.

RE: your questions:

• I have no objection to this being one PR; it's of a reasonable size and complexity to review in one go.
• These should be closed modules. I'm not 100% sure why some of the existing ones are open, but it's likely historical (and would be a breaking change to fix).

[HT154]

Reading the plugin source, it appears that all of these properties are actually required:

Suggested change

	/// The command to send to the Redis server, given as the command name
	/// followed by its arguments.
	///
	/// For example, `new { "get"; "sample-key" }`.
	command: Listing<String>?
	/// The field to store the result in.
	field: String?
	/// The type of the result.
	type: "string" | "integer" | "float" | Null
	/// The command to send to the Redis server, given as the command name
	/// followed by its arguments.
	///
	/// For example, `new { "get"; "sample-key" }`.
	command: Listing<String>
	/// The field to store the result in.
	field: String
	/// The type of the result.
	type: "string" | "integer" | "float"

[in-the-mood-for-mov]

Thank you for the review, I updated the PR. One question I had that I forgot to ask : for properties such as RedisInput.Servers, I considered using a Listing<Uri>? (with URI from pkl.experimental.uri, not the type alias in base), but decided not to because it would add a dependency. What do you think?

[bioball]

Yeah, it makes sense to use what's available in the stdlib rather than pkl.experimental.uri (that module provides a parser and a structured way to define URIs).

[bioball]

LGTM, this is great, thank you!