docs(installation): fix PyPI install Python version and OS deps

The PyPI install page claimed Python 3.12 (Ubuntu 24.04 default) was
unsupported and steered users to a deadsnakes 3.11 workaround. pyproject.toml
declares support for 3.10-3.12 (requires-python >=3.10), so the claim was
wrong and the workaround unnecessary.

- Drop the "3.12 not supported" claim and the deadsnakes/python3.11 steps
- Collapse the redundant Ubuntu blocks into one (tested 20.04/22.04/24.04),
  removing the EOL "before 20.04" block with its py2-era package names
- Point at pyproject.toml for supported versions (consistent with macOS section)
- Align OS deps with the repo Dockerfile: add python3-venv (needed by
  `python3 -m venv`), pkg-config (mysqlclient build), and libpq-dev (Postgres)
- Fix stale py2 package names in the yum block (python-devel ->
  python3-devel, etc.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/admin_docs/installation/pypi.mdx

@@ -22,31 +22,24 @@ level dependencies.
 
 **Debian and Ubuntu**
 
-Ubuntu **24.04** uses python 3.12 per default, which currently is not supported by Superset. You need to add a second python installation of 3.11 and install the required additional dependencies.
-```bash
-sudo add-apt-repository ppa:deadsnakes/ppa
-sudo apt update
-sudo apt install python3.11 python3.11-dev python3.11-venv build-essential libssl-dev libffi-dev libsasl2-dev libldap2-dev default-libmysqlclient-dev
-```
-
-In Ubuntu **20.04 and 22.04** the following command will ensure that the required dependencies are installed:
+The following command will ensure that the required dependencies are installed (tested on Ubuntu 20.04, 22.04, and 24.04):
 
 ```bash
-sudo apt-get install build-essential libssl-dev libffi-dev python3-dev python3-pip libsasl2-dev libldap2-dev default-libmysqlclient-dev
+sudo apt-get install build-essential libssl-dev libffi-dev python3-dev python3-pip python3-venv libsasl2-dev libldap2-dev libpq-dev default-libmysqlclient-dev pkg-config
 ```
 
-In Ubuntu **before 20.04** the following command will ensure that the required dependencies are installed:
-
-```bash
-sudo apt-get install build-essential libssl-dev libffi-dev python-dev python-pip libsasl2-dev libldap2-dev default-libmysqlclient-dev
-```
+Refer to the
+[pyproject.toml](https://github.com/apache/superset/blob/master/pyproject.toml) file for the list of
+Python versions officially supported by Superset, and install a matching `python3` interpreter for
+your distribution. The `libpq-dev` package is only needed if you intend to connect to (or use) a
+PostgreSQL database; you can omit it otherwise.
 
 **Fedora and RHEL-derivative Linux distributions**
 
 Install the following packages using the `yum` package manager:
 
 ```bash
-sudo yum install gcc gcc-c++ libffi-devel python-devel python-pip python-wheel openssl-devel cyrus-sasl-devel openldap-devel
+sudo yum install gcc gcc-c++ libffi-devel python3-devel python3-pip python3-wheel openssl-devel cyrus-sasl-devel openldap-devel
 ```
 
 In more recent versions of CentOS and Fedora, you may need to install a slightly different set of packages using `dnf`: