docs: add how-to for storing state

[tonyandrewmeyer]

This continues the previous work in moving chapters of the tutorial to how-to guides.

The how-to guide covers:

• Storing state with StoredState objects
• Storing state in a peer relation

Minor tweaks are also made to the "stored state uses and limitations" explanation doc, to which the how-to links.

[james-garner-canonical]

I've given this a read through and it looks good. I guess there will be corresponding PR(s) on the tutorial itself eventually too?

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Note: The test failure is unrelated to this PR.

[tonyandrewmeyer]

I guess there will be corresponding PR(s) on the tutorial itself eventually too?

Yes, e.g. #1511

[dwilding]

It's good to me, thanks Tony! I added one minor comment about a link.

[dwilding]

@tonyandrewmeyer I was just speaking with Dora and she mentioned that she's ready to come and update the links to point to new locations for Juju and Charmcraft docs. So maybe it would be better to leave the links in the source for now, to make that job easier?

[tonyandrewmeyer]

@tonyandrewmeyer I was just speaking with Dora and she mentioned that she's ready to come and update the links to point to new locations for Juju and Charmcraft docs. So maybe it would be better to leave the links in the source for now, to make that job easier?

The other "update links" comments were ones that Dora added, so I think that making them like this makes it easier for her to find and update them all. 🤞