📖 Improve provider definition in the glossary

[fabriziopandini]

What this PR does / why we need it:

This PR updates the definition of provider in the glossary to include all the components that can be deployed and provides a functionality to the Cluster API management Cluster.

This acknowledges the fact that we are already using this term for many things including core provider, infra provider, bootstrap and CP providers, and makes this suitable for including IPAM providers, Cluster add-on providers, Runtime Extension providers (which is a new term being defined in the Runtime SDK proposal).

If this is accepted, this will allow us to benefit of all the clusterctl machinery and provide a consistent UX for the users

[fabriziopandini]

/hold
for office hours discussion

[fabriziopandini]

/hold cancel
from the office hours discussion It seems there is a general consensus about the idea
I'm going to check the book to make sure we are using updated terms consistently, and finally remove wip

[fabriziopandini]

made a pass on the book ensuring terms are used consistently
now this PR is ready for review

[sbueringer]

Just nits, otherwise lgtm

[sbueringer]

lgtm pending squash

[killianmuldoon]

Good changes IMO.

Just a bunch of nits and rewordings in my review, none of them blocking.

[sbueringer]

Thx!
/lgtm

[killianmuldoon]

/lgtm

[sbueringer]

/lgtm

[sbueringer]

@fabriziopandini Should we merge or do we want to wait a bit longer?

[vincepri]

/approve

[k8s-ci-robot]

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[sbueringer]

/cherry-pick release-1.2

[k8s-infra-cherrypick-robot]

@sbueringer: new pull request created: #7326

In response to this:

/cherry-pick release-1.2

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