feat(cli): complete --config and --color before command

[nspin]

What does this PR try to resolve?

Split from #16245 (see #16245 (comment)).

Currently, cargo.bashcomp.sh supports completing values for --color and --config only in cases where they appear after the subcommand. This PR add support for completing values for these two flags when they appear before the subcommand.

How to test and review this PR?

In a Bash shell, run:

source src/etc/cargo.bashcomp.sh

Before this patch, the following behaves as expected (suggests colors or paths):

cargo build --co<tab>
cargo build --config <tab>

but the following does not behave as expected (colors or paths are not suggested):

cargo --config <tab>
cargo --color <tab>

With this patch applied, all of the following behave as expected:

cargo --config <tab>
cargo --color <tab>
cargo build --co<tab>
cargo build --config <tab>

[rustbot]

r? @epage

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Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @ehuss, @epage, @weihanglo
• @ehuss, @epage, @weihanglo expanded to ehuss, epage, weihanglo
• Random selection from ehuss, epage, weihanglo

[weihanglo]

This is nice. I feel like there are more global options that we might want to have such kind of completions. Not a blocker though.