feat: Create endpoint for fetching the flux namespace

[yitsushi]

Add new endpoint to query flux namespace. For simplicity, no arguments
on the request and returns only the name of the namespace. That fulfills
the original request so we can remove the constant¹ from the UI.

== Considered solutions

1. Create a general endpoint

The consumer could query namespaces and filter them with provided
filters.

Dropped this solution, because it could open up some weird surfaces
where the client can query arbitrary filters.

2. Create a general endpoint with strict filtering options

The consumer could query namespaces with a set of filter options and if
they are not specified, throw back an error.

Dropped this solution, because changing the filtering rules would
require code change. The final solution in this change-set has the same
issue, but less complex. If we don't get extra value out of the
complexity, it's not worth it.

== Follow-up

If/when we need a complex endpoint to query all namespaces with filter
options, then we can add one with a plan like:

• Who/what will use it?
• What is the desired input and output?
• How to achieve this?
• What limitations do we want to implement?
• How much freedom do we want to give to the consumer?

== Other changes

• make proto updated a lot of auto-generated files.

• In tools/dependencies.toml, removed the system-wide installation of
  a tool, because the last thing I want from a project to download a
  binary and place it somewhere with root permission. I'm not giving
  root permissions just to install dependencies.

• Use tools/bin/tilt in Makefile (see previous entry).

• Replaced the logic behind getMatchingLabels. Using the with option
  pattern, we can build up more complex labeling queries, and the
  codebase will remain clean.

  match := matchLabel(
    withPartOfLabel(appName),
    withInstanceLabel(appInstance),
    withManagedByLabel(appManager),
  )

Closes #1465

Footnotes

1. https://github.com/weaveworks/weave-gitops/pull/1451/files#diff-35acf2adc3a7b1021fb41d3473b47e030d3708ba2e8ff7a4b76c13ee80b4076cR42 ↩

[yitsushi]

Created a new PR, because the previous one was created from my fork and my fork does not have some secrets for PR checkers.

[jpellizzari]

Assuming it is the same, LGTM 👍

Nice work on the PR description. Very informative.

This PR will probably cause some conflicts: #1489

It moves things to a fluxruntime.go file.