Use cascade variable for Grafana Agent Flow name

[clayton-cornell]

PR Description

This PR adds in a cascade variable for the Grafana Agent Flow product name in the documentation.

Two cascade variables are declared:

• PRODUCT_NAME = Grafana Agent Flow
• PRODUCT_ROOT_NAME = Grafana Agent

I used two variables here because there is crossover between Static, Flow, and Operator. Some of the text refers to Grafana Agent in general, and some refers to Grafana Agent Flow (content that is specific to Flow). Using PRODUCT_ROOT_NAME is an easy future proofing way to deal with this without rewriting the text. When the time comes to only use a single product name, it will be easy to grep for the variable and update the topics.

ToDo:

• Update top level topics
• Update Concepts
• Update Configuration Language
• Update Getting Started
• Update Monitoring
• Update Reference
• Update Setup
• Update Tutorials
• Update shared content
• Search for and fix any missed Grafana Agent, Grafana Agent Flow, Grafana Agent in Flow mode, Flow mode, Flow and other variations on the product name. There are MANY cases where agent is used as a general term for Grafana Agent Static/Operator/Flow (sometimes one of these, sometimes combinations of these)
• Validate/check/review changes to make sure the wording still makes sense and the correct form of the product name is used

Which issue(s) this PR fixes

Notes to the Reviewer

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated

[spartan0x117]

Similar to previous comment (so feel free to ignore if this is intended), but looks like the numbers were all set to 1. in this ordered list.

[clayton-cornell]

Markdown ignores the numbers.. most of the time :-) and numbers the list in sequential order. We suggest to use lazy numbering. I update to lazy when I pass over topics. It's not a must...

[jdbaldry]

Cool stuff!

Didn't see anything odd at a scan. Let me know if you want a more in-depth check.

If we start running doc-validator on these docs, we'll need to make that tool front matter aware because it would understand the H1s to be the literal string.

[clayton-cornell]

If we start running doc-validator on these docs, we'll need to make that tool front matter aware because it would understand the H1s to be the literal string.

doc-validator in the Agent repo needs a big update anyway. I'm using it, but it generates a lot of false positives right now. A thing for a separate PR. :-)

[grafanabot]

The backport to release-v0.38 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-5879-to-release-v0.38 origin/release-v0.38
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x af8bced391c91505d6962c44463aced76edbd4cd
# Push it to GitHub
git push --set-upstream origin backport-5879-to-release-v0.38
git switch main
# Remove the local backport branch
git branch -D backport-5879-to-release-v0.38

Then, create a pull request where the base branch is release-v0.38 and the compare/head branch is backport-5879-to-release-v0.38.