Support Symfony 8

[nikow13]

No description provided.

[kimpepper]

Thanks for this PR @nikow13

A couple of things to fix up:

• You need to sign your commits with --signoff. See the failure message on https://github.com/opensearch-project/opensearch-php/pull/381/checks?check_run_id=58085454339
• You need to update CHANGELOG.md and add an entry about Symfony v8.0.0 support

[kimpepper]

Commented above