Added documentation for ActiveRecord::Relation#pick [skip ci]

[soartec-lab]

Motivation / Background

This Pull Request has been created because there is no explanation of ActiveRecord::Relation#pick in the guide.

Detail

This Pull Request changes to add the documentation for ActiveRecord::Relation#pick to the guide.

Additional information

• api url: https://edgeapi.rubyonrails.org/classes/ActiveRecord/Calculations.html#method-i-pluck
• edge guide url: https://edgeguides.rubyonrails.org/active_record_querying.html#pluck

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[p8]

Suggested change

	pick is a short-hand for `relation.limit(1).pluck(*column_names).first`, which makes it possible to replace code like:
	`pick` is a short-hand for `relation.limit(1).pluck(*column_names).first`, which makes it possible to replace code like:

[soartec-lab]

i will handle this.

[soartec-lab]

I fixed https://github.com/rails/rails/pull/48404/files#diff-77236751c3ab97b753f641ae6e10445de7662826f0176c68b5176feec92d0a1bR2263

[soartec-lab]

I also created a PR to change the ActiveRecord::Relation#pluck guide.

#48465

[soartec-lab]

@p8
Thank you for your review.
I have corrected what you pointed out.
could you to review again?

[p8]

I think this was copied and modified from the documentation of pluck.
The explanation in the API docs is a lot clearer to me.
What do you think about using some of the API docs wording?
For example:

Suggested change

	[`pick`][] can be used to query single or multiple columns from the underlying table of a model. It accepts a list of column names as an argument and returns the first one of the specified column values ​​with corresponding data type.
	[`pick`][] can be used to pick the value(s) from the named column(s) in the current relation. This is primarily useful when you have a relation that’s already narrowed down to a single row. It accepts a list of column names as an argument and returns the first one of the specified column values ​​with corresponding data type.

PS. I'd also accept a seperate PR to reword the first paragraph of pluck to something more similar to the API docs.

[soartec-lab]

sounds good!
Indeed, I would change this as I thought the wording in the API docs was clearer.
And, I will create a separate PR for changes to pluck

[soartec-lab]

Supported by 900bf10

Changed the description to use some of the wording from the API documentation. Also, Added nuances to the main useful cases.

[p8]

The example shows how easy it is to shorten the code with pick.
But I think it misses the nuance that pick "is primarily useful when you have a relation that’s already narrowed down to a single row.".

Suggested change

	```ruby
	Customer.limit(1).pluck(:id).first
	```
	with:
	```ruby
	Customer.pick(:id)
	```
	```ruby
	Customer.where(id: 1).pluck(:id).first
	```
	with:
	```ruby
	Customer.where(id: 1).pick(:id)
	```

[soartec-lab]

Indeed, an important nuance was missing. I will reflect the suggested source code.

[soartec-lab]

Supported by 9904db0

[soartec-lab]

@p8

Thanks for your review.
I have reflected the suggestions you gave me.
In addition, the ActiveRecord::Relation#pluck guide is also addressed in #48465.

Please check it out.

[soartec-lab]

@p8

thank you for making sure.I have modified your last suggestion.
I also squashed all commits.

[p8]

Thanks @soartec-lab !