Update to Bevy 0.19

[TotalKrill]

Updates bevy_mod_reqwest for Bevy 0.19 compatibility.

Changes:

• Bump crate version to 0.22.0
• Bump Bevy dependency to 0.19
• Update README compatibility table and changelog
• Remove a clippy map_identity warning in request polling

Verified locally:

• cargo fmt --check
• cargo test --all-targets --all-features
• cargo clippy --all-targets --all-features -- -D warnings
• timeout 15s cargo run --example minimal
• timeout 15s cargo run --example json
• timeout 15s cargo run --example post