Clarify conda_id docs

[traversaro]

What kind of change does this PR introduce?

• Bugfix
• New Feature
• Feature Improvement
• Refactoring
• Documentation
• Other, please describe:

Description:

While reading the conda_id documentation, I was a bit confused, especially by the "If the main package is provided on a different channel" string, as it was not clear to me what "different channel" meant. By looking into the code, I understood that the "default" channel is the anaconda one, and if you are referring to another channel, you need to indicate it, so I tried to clarify the docs (I am not sure I was able to do that).

More in general, I think that pointing users to the anaconda channel by default is a bit risky as that channel is not free to use (see https://www.theregister.com/2024/08/08/anaconda_puts_the_squeeze_on/ and https://thehftguy.com/2025/04/07/anaconda-inc-has-entered-litigation-against-non-paying-user-of-anaconda-alibaba-intel-dell-airbus/), but this is another story.

I also changed the link for the conda package manager to point to the home page of the open source conda project, and not to the anaconda company, that are two different entities (even if historically related).

Checklist:

• I have read the CONTRIBUTING document.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[traversaro]

fyi @knmcguire