docs: Update install docs for v25.02

[chrisguida]

Also removes usage of pip due to this error that crops up on newer versions of Ubuntu:

error: externally-managed-environment

× This environment is externally managed
╰─> To install Python packages system-wide, try apt install
    python3-xyz, where xyz is the package you are trying to
    install.

    If you wish to install a non-Debian-packaged Python package,
    create a virtual environment using python3 -m venv path/to/venv.
    Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make
    sure you have python3-full installed.

    If you wish to install a non-Debian packaged Python application,
    it may be easiest to use pipx install xyz, which will manage a
    virtual environment for you. Make sure you have pipx installed.

    See /usr/share/doc/python3.12/README.venv for more information.

note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.

I've been recommending installing Poetry from the official installer for the past several months and it always works.

Changelog-None

Important

25.02 FREEZE JANUARY 31ST: Non-bugfix PRs not ready by this date will wait for 25.05.

Checklist

Before submitting the PR, ensure the following tasks are completed. If an item is not applicable to your PR, please mark it as checked:

• The changelog has been updated in the relevant commit(s) according to the guidelines.
• Tests have been added or modified to reflect the changes.
• Documentation has been reviewed and updated as needed.
• Related issues have been listed and linked, including any that this PR closes.

[vincenzopalazzo]

ACK 3128fd3

[chrisguida]

rebased on master

@ShahanaFarooqui this is ready for re-review!

related: #8161

[chrisguida]

@daywalker90 @ZenenTreadwell would love an ACK here :)

[ZenenTreadwell]

ACK 07c9c8e

I am ambivalent about poetry as a package manager - I much prefer using the standard venv package - but seeing as it is already integrated into CLN's installation process, I think that having it properly documented is a good thing.

+1 to everything else for improving readability and keeping things updated

[endothermicdev]

I think it's also time to clean up the poetry shell part as that command is removed from 2.0 onward, but this looks good.
ACK 07c9c8e

[chrisguida]

@endothermicdev thanks for the review!

Are you planning to make the mentioned edits to the poetry shell stuff or should I? Sounds like you have a pretty good idea of what you want to see?

[endothermicdev]

I can do that in another PR.