feat: add custom headers to search api requests

[underchemist]

Description

This PR adds a --header option to the search subcommand which are passed to the reqwest::ClientBuilder::default_headers method. The intended use case is to enable the passing of custom headers to requests made by the rustac STAC api client e.g. Authorization headers.

This adds a new ApiClientBuilder struct which wraps reqwests::ClientBuilder in order to manage adding creating a Client instance with default headers.

I used copilot to help me in my approach.

Checklist

Delete any checklist items that do not apply (e.g. if your change is minor, it may not require documentation updates).

• Unit tests
• Documentation, including doctests
• Pull request title follows conventional commits
• Pre-commit hooks pass (prek run --all-files)

[underchemist]

I'm not familiar enough with rust ecosystem to interpret the msrv failure. To me this appears to be an issue compiling a third-party crate. If there is something that needs to be addressed for that let me know.

[gadomski]

Should be fixed by #944 🤞🏼

[gadomski]

This is great, thanks!