WIP: Feature for editing existing Discord Message

[yutamago]

WIP: needs testing

• Added functionality to edit or replace an existing message.

• Added 2 new optional input paramters:

  • updateMessageMode
    Specifies if and how you want to update an already existing message.
    none does not update an existing message, edit modifies an existing message, replace deletes an existing message and creates a new one.
    Default: none
  • updateMessageId
    Specifies which message to update. Defaults to environment variable discordWebhookLastMessageId, which is automatically set when a message is successfully created.
    If you need the messageId from another job or stage, you could utilize the output variable discordWebhookMessageId, which is also set by this task.

• Added output variable: discordWebhookMessageId
  Automatically set to the message ID when successful. Can be used across stages/jobs. Requires the task to be named.

• Added environment variable: discordWebhookLastMessageId
  Automatically set to the message ID when successful. Can be used within the same stage.

• Added tests.