[Document] Add discussion about vector lifecycle

[asfimport]

As discussed in https://issues.apache.org/jira/browse/ARROW-7254?focusedCommentId=16983284&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-16983284, we need a discussion about the lifecycle of a vector.

Each vector has a lifecycle, and different operations should be performed in particular phases of the lifecycle. If we violate this, some unexpected results may be produced. This may cause some confusion for Arrow users. So we want to add a new section to the prose document, to make it clear and explicit.

Reporter: Liya Fan / @liyafan82
Assignee: Liya Fan / @liyafan82

PRs and other links:

• GitHub Pull Request #5969

_{Note: This issue was originally created as ARROW-7277. Please see the migration documentation for further details.}

[asfimport]

Micah Kornfield / @emkornfield:
Issue resolved by pull request 5969
#5969