Fix documentation for 2nd Batch callback parameter: consistently call…

… it `context` (#1476)

* Fix batch `options` => `params` in README.md

* Use `context` to describe second batch callback job argument

* Fix code example to use `context`

* Fix one more usage for `context`

---------

Co-authored-by: Ben Sheldon [he/him] <bensheldon@gmail.com>

README.md

@@ -681,15 +681,15 @@ Batches track a set of jobs, and enqueue an optional callback job when all of th
  OtherJob.perform_later
  end
 
- # When these jobs have finished, it will enqueue your `MyBatchCallbackJob.perform_later(batch, options)`
+ # When these jobs have finished, it will enqueue your `MyBatchCallbackJob.perform_later(batch, context)`
  class MyBatchCallbackJob < ApplicationJob
- # Callback jobs must accept a `batch` and `options` argument
- def perform(batch, params)
+ # Callback jobs must accept a `batch` and `context` argument
+ def perform(batch, context)
  # The batch object will contain the Batch's properties, which are mutable
  batch.properties[:user] # => <User id: 1, ...>
 
- # Params is a hash containing additional context (more may be added in the future)
- params[:event] # => :finish, :success, :discard
+ # Context is a hash containing additional context (more may be added in the future)
+ context[:event] # => :finish, :success, :discard
  end
  end
  ```
@@ -757,19 +757,19 @@ Batch callbacks are Active Job jobs that are enqueued at certain events during t
 - `:success` - Enqueued only when all jobs in the batch have finished and succeeded.
 - `:discard` - Enqueued immediately the first time a job in the batch is discarded.
 
-Callback jobs must accept a `batch` and `params` argument in their `perform` method:
+Callback jobs must accept a `batch` and `context` argument in their `perform` method:
 
 ```ruby
 class MyBatchCallbackJob < ApplicationJob
- def perform(batch, params)
+ def perform(batch, context)
  # The batch object will contain the Batch's properties
  batch.properties[:user] # => <User id: 1, ...>
  # Batches are mutable
  batch.properties[:user] = User.find(2)
  batch.save
 
- # Params is a hash containing additional context (more may be added in the future)
- params[:event] # => :finish, :success, :discard
+ # Context is a hash containing additional context (more may be added in the future)
+ context[:event] # => :finish, :success, :discard
  end
 end
 ```
@@ -811,7 +811,7 @@ class WorkJob < ApplicationJob
 end
 
 class BatchJob < ApplicationJob
- def perform(batch, options)
+ def perform(batch, context)
  if batch.properties[:stage].nil?
  batch.enqueue(stage: 1) do
  WorkJob.perform_later('a')