[nextion] Adds a command pacer with command_spacing attribute

[edwardtfn]

Description:

This introduces a "pacer" for the communication with the Nextion display, with the main objective to reduce the chances of a buffer overflow on Nextion side.
The buffer overflow can be quite critical, as it removes it's queue, while the component on ESPHome keeps waiting for responses for those removed commands, so a way to control the communication pace and give to users a chance to reduce the chances of a buffer overflow by compromising (a bit?) the performance which many times wouldn't be perceived by end users.
As default I'm setting the pace to 0ms, to keep this transparent to existing installation, although I would highly recommend the use of at least 10ms. Anyhow, users can increase this dynamically, if a buffer overflow happens.

Related issue (if applicable): N/A

Pull request in esphome with YAML changes (if applicable): esphome/esphome#7948

Checklist:

• I am merging into next because this is new documentation that has a matching pull-request in esphome as linked above.
  or

• I am merging into current because this is a fix, change and/or adjustment in the current documentation and is not for a new component or feature.

• Link added in /index.rst when creating new documents for new components or cookbook.

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