[Request]: Standardize on using "app" instead of "UI" when talking about parts of the Observability UI

[dedemorton]

Description

We've decided to follow the convention of using "UI" instead of "app" but still have some docs that use "app". We just need to do a cleanup. Note that "app" is still used in the shared asciidoc attributes, so whoever owns this issue should initiate a docs-wide conversation: https://github.com/elastic/docs/blob/master/shared/attributes.asciidoc

I'm modifying the title and description here because (interestingly enough) the guidelines that cover writing about the UI say to use app: https://docs.elastic.dev/tech-writing-guidelines/ui-writing#kibana-labeled

Resources

n/a

Which documentation set does this change impact?

Stateful and Serverless

Feature differences

Same in stateful and serverless

What release is this request related to?

N/A

Collaboration model

The documentation team

Point of contact.

Main contact: @bmorelli25

Stakeholders:

[dedemorton]

@bmorelli25 I'm just going to close this because a) looking at our docs across various products, there's not a lot of consistency right now anyhow, b) this is low priority and doesn't affect usability of docs, and c) rather than making changes manually (it's not a simple search/replace), we should use a linter and automate some of the cleanup (plus linting is a better way to enforce style issues over time).

Feel free to reopen this issue if you feel otherwise.