Drop support for Symfony versions <5.4

[glaubinix]

Q	A
Bug fix?	no
New feature?	no
BC breaks?	no
Deprecations?	no
Related tickets	addresses a part of #439 (comment)
Documentation	if this is a new feature, link to pull request in https://github.com/php-http/documentation that adds relevant documentation
License	MIT

What's in this PR?

Drops support for Symfony version <5.4

Why?

Symfony 4.4 only receives security updates. Current LTS is 5.4 and will soon be 6.4.

Checklist

• Updated CHANGELOG.md to describe BC breaks / deprecations | new feature | bugfix
• Documentation pull request created (if not simply a bugfix)

To Do

• I think I got everything but in case I missed something let me know

[dbu]

awesome, thank you!