Add change_column_comment and change_table_comment table schema definition

[mechnicov]

Motivation / Background

This Pull Request has been created because these methods are missing, but could be helpful for bulk changes of the table. This will allow you to add comment(s) to the table and/or to the column(s) using single block, improving readability and performance because of single query

Detail

This Pull Request adds change_column_comment and change_table_comment for change_table definition

change_table :users, bulk: true do |t|
  t.change_column_comment :login, "Username"
  t.change_table_comment "Usual users"
end

Additional information

This was intended as non-breaking change

Checklist

• This Pull Request is related to one change. Unrelated changes 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.

[mechnicov]

May be t.column_comment (or just t.comment) and t.table_comment is better

[mechnicov]

Hello @rafaelfranca

I see you merged similar commit

f84e1eb

Please review my PR as well. Thank you