Add syntax highlighting to examples in ockam command help.

[mrinalwadhwa]

Currently

In the help for various ockam command we're adding examples.

For example ockam

Also try:

ockam secure-channel create --help

Desired

The examples section, which is usually made of shell commands, we want to make it have colors.
Syntect seems like a good crate to use for this, but there may be others
https://crates.io/crates/syntect

The code for the above example is here https://github.com/build-trust/ockam/blob/develop/implementations/rust/ockam/ockam_command/src/lib.rs#L64-L77

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[mrinalwadhwa]

Added in #3364
Thank you @jlucktay 🥁