docs(entity): clarify how entities update

[AdditionAddict]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• [x ] Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

What is the new behavior?

user.actions.ts

• Differentiate the updateOne and updateMany which use the Update<T> interface by using props update/updates over user/users
  Closes Entities updateOne documentation inaccurate? #2431

Add section Entity Updates clarifying how entities update under various adapter methods.
Many issues have been raised with regards to this #1604, #2061, #2369

Does this PR introduce a breaking change?

[ ] Yes
[x ] No

Other information

[ngrxbot]

Preview docs changes for 2e47ff5 at https://previews.ngrx.io/pr2432-2e47ff5/

[kameelyan]

Love the changes!