[1.2.x] Fix concurrent issue in observability

[NipunaMadhushan]

Purpose

Due to high throughput of inprogress requests, we have been notified that the http_inprogress_requests_value metric value is higher than the expected value.

There is a observer context list (HashMap) which contains the observer contexts with span IDs as keys. since it is updated with multiple threads concurrently, it resulted in incorrect calculations of new array sizes, including negative sizes for the HashMap.

Therefore HashMap has been replaced with ConcurrentHashMap which is a thread-safe implementation. With this approach, multiple threads can access it simultaneously without any synchronization issues.

Fixes https://github.com/wso2-enterprise/internal-support-ballerina/issues/679

Approach

Describe how you are implementing the solutions along with the design details.

Samples

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Remarks

List any other known issues, related PRs, TODO items, or any other notes related to the PR.

Check List

• Read the Contributing Guide
• Updated Change Log
• Checked Tooling Support (#)
• Added necessary tests
  • Unit Tests
  • Spec Conformance Tests
  • Integration Tests
  • Ballerina By Example Tests
• Increased Test Coverage
• Added necessary documentation
  • API documentation
  • Module documentation in Module.md files
  • Ballerina By Examples

[warunalakshitha]

Can we add test cases for these cases?

[NipunaMadhushan]

Can we add test cases for these cases?

Since these scenarios came only with high throughput in MG, I really doubt if it is possible as a Java test case.

[warunalakshitha]

LGTM