Docs: Easier method for linking to subheadings

[jkfran]

From canonical/juju.is#303:

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It would be nice if there was a way to link to a heading in a docs page - e.g. I've just said to someone in https://chat.charmhub.io/charmhub/channels/charm-dev:

"""see the "Peer relation example" section of https://juju.is/docs/sdk/relations."""

The link already exists, as https://juju.is/docs/sdk/relations#heading--peer-relations but it is a bit hidden. To find that you have to right click the header -> inspect element -> look the HTML code for the id tag. It'd be nice if there was a visual element that let you copy that link.

[anthonydillon]

I've requested a Vanilla pattern to for this behaviour: canonical/vanilla-framework#3863.

[carkod]

Is this maybe a duplicate of this?