in_elasticsearch: provide version parameter for configurable server version

[cosmo0920]

Currently, in_elasticsearch just returns elasticasearch server version as 8.0.0.
Some of elasticsearch/opensearch clients wants to newer version of its server.
This PR provides configurable option for elasticsearch server version.

---

Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change

$ bin/fluent-bit -i elasticsearch -p port=9880 -pversion=8.1.2 -o stdout

Another terminal

$ curl localhost:9880/
{"version":{"number":"8.1.2","build_flavor":"Fluent Bit OSS"},"tagline":"Fluent Bit's Bulk API compatible endpoint"}

• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

==189199== 
==189199== HEAP SUMMARY:
==189199==     in use at exit: 95,170 bytes in 702 blocks
==189199==   total heap usage: 2,842 allocs, 2,140 frees, 1,548,728 bytes allocated
==189199== 
==189199== LEAK SUMMARY:
==189199==    definitely lost: 0 bytes in 0 blocks
==189199==    indirectly lost: 0 bytes in 0 blocks
==189199==      possibly lost: 0 bytes in 0 blocks
==189199==    still reachable: 95,170 bytes in 702 blocks
==189199==         suppressed: 0 bytes in 0 blocks
==189199== Reachable blocks (those to which a pointer was found) are not shown.
==189199== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==189199== 
==189199== For lists of detected and suppressed errors, rerun with: -s
==189199== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• Documentation required for this feature

fluent/fluent-bit-docs#1135

Backporting

• Backport to latest stable release.

---

Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.