Update drop, respond, and sequence mediator docs

[chanikag]

Purpose

This PR is to update

1. Drop mediator
2. Respond Mediator
3. Sequence Mediator

pages

Goals

Describe the solutions that this feature/fix will introduce to resolve the problems described above

Approach

Describe how you are implementing the solutions. Include an animated GIF or screenshot if the change affects the UI (email documentation@wso2.com to review all UI text). Include a link to a Markdown file or Google doc if the feature write-up is too long to paste here.

User stories

Summary of user stories addressed by this change>

Release note

Brief description of the new feature or bug fix as it will appear in the release notes

Documentation

Link(s) to product documentation that addresses the changes of this PR. If no doc impact, enter “N/A” plus brief explanation of why there’s no doc impact

Training

Link to the PR for changes to the training content in https://github.com/wso2/WSO2-Training, if applicable

Certification

Type “Sent” when you have provided new/updated certification questions, plus four answers for each question (correct answer highlighted in bold), based on this change. Certification questions/answers should be sent to certification@wso2.com and NOT pasted in this PR. If there is no impact on certification exams, type “N/A” and explain why.

Marketing

Link to drafts of marketing content that will describe and promote this feature, including product page changes, technical articles, blog posts, videos, etc., if applicable

Automation tests

• Unit tests

  Code coverage information

• Integration tests

  Details about the test cases and coverage

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines? yes/no
• Ran FindSecurityBugs plugin and verified report? yes/no
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes/no

Samples

Provide high-level details about the samples related to this feature

Related PRs

List any other related PRs

Migrations (if applicable)

Describe migration steps and platforms on which migration has been tested

Test environment

List all JDK versions, operating systems, databases, and browser/versions on which this feature/fix was tested

Learning

Describe the research phase and any blog posts, patterns, libraries, or add-ons you used to solve the problem.

[DinithiDiaz]

Shall we explain this example a bit more for clarity? I think we can use a similar approach to the original text to explain the use case.