Improve GitHub actions

[pentamassiv]

This PR improves the Github Action in a couple of ways:

• Fixed failed clippy action
• actions-rs/toolchain was unmaintained and the repo has been archived. It was replaced with dtolnay/rust-toolchain, which seems like the new standard action
• Restricted the permissions of the Github Token used by the Action
• Added dependabot to keep the dependencies of the crate updated and additionally check the versions of the actions used in the Github Workflow
• Allow manually triggering the workflow
• Check the clippy lints for the crate, the examples and the tests
• Make sure the crate builds on the MSRV, stable, nightly and beta
• Make sure the docs build

[pentamassiv]

Looks like the MSRV needs to be increased. The CI fails to build the crate with the following error:

warning: /home/runner/work/xkeysym/xkeysym/Cargo.toml: unused manifest key: package.rust-version
    Updating crates.io index
 Downloading crates ...
  Downloaded quote v1.0.33
  Downloaded bytemuck_derive v1.5.0
  Downloaded proc-macro2 v1.0.69
error: failed to parse manifest at `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.69/Cargo.toml`

Caused by:
  failed to parse the `edition` key

Caused by:
  this version of Cargo is older than the `2021` edition, and only supports `2015` and `2018` editions.
Error: Process completed with exit code 101.

Rust 1.48 is "ancient" so there probably aren't many people relying on that version anymore. Should be fine to be increased

[notgull]

Testing indicates that the MSRV for the master branch is 1.58.1. Do you mind bumping the MSRV to there in this PR?

[pentamassiv]

Sure, done

[notgull]

Thanks!