Add only configuration option to todo rule

[gibachan]

Resolves #5232

This PR adds an only configuration option to the todo rule.
This option allows you to choose whether only FIXME or TODO will be warned.

[SwiftLintBot]

	17 Messages
📖	Linting Aerial with this PR took 1.19s vs 1.2s on main (0% faster)
📖	Linting Alamofire with this PR took 1.56s vs 1.56s on main (0% slower)
📖	Linting Brave with this PR took 8.92s vs 8.92s on main (0% slower)
📖	Linting DuckDuckGo with this PR took 4.45s vs 4.44s on main (0% slower)
📖	Linting Firefox with this PR took 10.38s vs 10.38s on main (0% slower)
📖	Linting Kickstarter with this PR took 11.49s vs 11.49s on main (0% slower)
📖	Linting Moya with this PR took 0.63s vs 0.63s on main (0% slower)
📖	Linting NetNewsWire with this PR took 3.35s vs 3.36s on main (0% faster)
📖	Linting Nimble with this PR took 0.83s vs 0.83s on main (0% slower)
📖	Linting PocketCasts with this PR took 8.83s vs 8.83s on main (0% slower)
📖	Linting Quick with this PR took 0.4s vs 0.4s on main (0% slower)
📖	Linting Realm with this PR took 11.73s vs 11.72s on main (0% slower)
📖	Linting Sourcery with this PR took 2.83s vs 2.85s on main (0% faster)
📖	Linting Swift with this PR took 5.28s vs 5.28s on main (0% slower)
📖	Linting VLC with this PR took 1.55s vs 1.54s on main (0% slower)
📖	Linting Wire with this PR took 9.13s vs 9.12s on main (0% slower)
📖	Linting WordPress with this PR took 13.26s vs 13.27s on main (0% faster)

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[SimplyDanny]

Thanks for taking this up!

[SimplyDanny]

Rebased, renamed property and moved changelog entry to new main section.

[grantneufeld]

Just a word of thanks, to both of you @gibachan and @SimplyDanny , for the speedy implementation of this requested feature. 💚