docs: add anchors and fix a few small things

[tmihoc]

This PR adds a few anchors that will be used through intersphinx in the Ops docs.

The PR also changes a couple of titles and adds some content. Also fixes a weird rendering error.

Note:

• The reason I've changed "Set up Charmcraft" to "Manage Charmcraft", as it used to be, is because that's the pattern we follow everywhere in Juju-world docs, the reason being that that docs doesn't just cover setup but should also cover upgrade and uninstall. I've added some content to that effect as well.
• For charm naming best practices we should at some point enhance that note to reflect, in streamlined fashion, all the crucial bits from https://discourse.charmhub.io/t/charm-naming-guidelines/5364#naming-charms-1 (this old Discourse post can then be discarded).

[lengau]

Thanks for the PR! Could you fix the linting errors? (You can check them locally with make lint-docs)

  Installed 78 packages in 94ms
  docs/howto/manage-charmcraft.rst:164: trailing whitespace (trailing-whitespace)
  docs/howto/manage-charms.rst:16: default role used (hint: for inline literals, use double backticks) (default-role)
  docs/howto/manage-charms.rst:93: default role used (hint: for inline literals, use double backticks) (default-role)
  docs/howto/manage-charms.rst:14: trailing whitespace (trailing-whitespace)
  docs/howto/manage-charms.rst:15: trailing whitespace (trailing-whitespace)
  docs/howto/manage-charms.rst:95: trailing whitespace (trailing-whitespace)
  docs/howto/manage-charms.rst:16: Line too long (156/88) (line-too-long)
  docs/howto/manage-charms.rst:93: Line too long (196/88) (line-too-long)
  make: *** [common.mk:155: lint-docs] Error 1

[tmihoc]

Thanks for the PR! Could you fix the linting errors? (You can check them locally with make lint-docs)

make lint-docs doesn't work for me. Also, I don't really understand the linting error messages. It would be good if we had a tool that could automatically fix things to satisfy the linter. Let's chat!

[tmihoc]

Fixed the linting errors.

PS I had to run make setup for make lint-docs to even run; had to ask for expert help to figure out what the error messages even meant; had to manually move content to the next line; and had to research and configure my editor to be able to even see the "errors" (trailing space and such). It shouldn't be this hard.

[medubelko]

Thanks, @tmihoc!

I'm providing one style suggestion and suggesting a few technical changes based on what I found in a local build.

[tmihoc]

The PR adding the missing anchors in Juju has been merged.

[medubelko]

LGTM. Safe to merge after the linter passes.