feat: added retention policy for v2 api

[stegaBOB]

Description

Added the ability to add a retention policy to the client parameters. Mainly for v2 compatibility, which uses the retention policy to map to bucket names https://docs.influxdata.com/influxdb/v2/reference/api/influxdb-1x/dbrp/

Checklist

• Formatted code using cargo fmt --all
• Linted code using clippy
  • with reqwest feature: cargo clippy --manifest-path influxdb/Cargo.toml --all-targets --no-default-features --features use-serde,derive,reqwest-client -- -D warnings
  • with surf feature: cargo clippy --manifest-path influxdb/Cargo.toml --all-targets --no-default-features --features use-serde,derive,hyper-client -- -D warnings
• Updated README.md using cargo doc2readme -p influxdb --expand-macros
• Reviewed the diff. Did you leave any print statements or unnecessary comments?
• Any unfinished work that warrants a separate issue captured in an issue with a TODO code comment

Note: Method of chrono got deprecated which is causing some linting to fail, but that's unrelated to this PR.

[Empty2k12]

Hello,

thanks for your contribution. Could you please also add tests for your feature?