Makes reqwest optional

[awesterb]

Which issue does this PR close?

Closes #723 .

Rationale for this change

We're using object_store with a code base that already uses awc as HTTP-client, and would like to avoid having reqwest as additional HTTP client alongside awc. An alternative HttpConnector can already be provided currently, but the reqwest dependency can not yet be avoided.

Also, since reqwest can't be used for wasm32-wasip1 anyways, not having to package it there is nice too.

What changes are included in this PR?

Adds a new reqwest feature that gates dep:reqwest, but is enabled by cloud by default. This means reqwest will still be pulled in by the azure, gcp, aws and http features, as is the case now. For avoiding reqwest, the features cloud-base, azure-base, gcp-base, aws-base and http-base are added.

Some features that depend on reqwest types I gated behind reqwest too, such as client::Certificate. To keep the pull request minimal and non-breaking, I did not attempt to rewrite those to be reqwest-independent. I believe all of the gated features can be avoided when providing your own HttpConnector. (Besides, most of these features were already gated behind !wasm32.)

Tests that use reqwest-gated types were gated behind reqwest too.

Added to CI extra clippy jobs to catch missing gates in the future, and a build job for wasm32-wasip1 without reqwest.

Where reqwest::{Method,StatusCode,header} was used, this was replaced by the http types.

I considered copying the X-no-crypto naming scheme (aws-no-crypto, gcp-no-crypto ...) from GH-707, but decided not to use aws-no-reqwest (etc.) since that would necessitate aws-no-crypto-no-reqwest (and worse) in the future. (Combining !707 could make sense, having X-base mean no crypto and no reqwest.)

Are there any user-facing changes?

The feature reqwest that gates dep:reqwest, and the features cloud-base, azure-base, gcp-base, aws-base and http-base that avoid reqwest.

No breaking changes (according to https://crates.io/crates/cargo-semver-checks.)