Cleanup Helm Chart documentation

[Miretpl]

During searching of possible things missed in #61018, I found a couple of more things in the Helm Chart docs and decided to fix some things. The changes consist of:

1. Rewriting some parts to be easier to follow
2. Add warnings regarding security concerns in some places
3. Make headers unified in terms of hierarchy
4. Update some links
5. In most cases, change webserver to apiServer
6. Remove some duplicated information between different sections
7. Remove information that KEDA is experimental (it is so long in the chart that I thought that maybe it is about time)
8. Finally..., remove some missed parts in the mentioned PR 😄

Edit: Additional things done:

1. Fix indent to match official Sphinx doc (3 spaces)
2. Change kubernetes to Kubernetes
3. Add a caption for almost all code blocks
4. Add missing language for code blocks

---

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

---

• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[jscheffl]

Very cool rework! Wow.

[jscheffl]

Cool!