Replace telco and operator by more general terms

[AxelNennker]

What type of PR is this?

• documentation

What this PR does / why we need it:

Generalize the terms telco and operator to API provider

Which issue(s) this PR fixes:

Partly fixes 200

[AxelNennker]

Please add suggestions or approve

[jpengar]

Please add suggestions or approve

@AxelNennker Before we finish the review and merge this PR into main, we need to create another PR to update the README and CHANGELOG files and generate the r0.2.1 patch release as suggested by @herbert in #196 (comment).

[AxelNennker]

Followed @tanjadegroot review comments - mostly. Resolved conversations.
If I did not resolve a conversation, then please review my comment on that conversation and decide whether it can be resolved or not.

[jpengar]

LGTM. We may need to make sure that the new DPV doc references are not broken again when we merge this PR. master branch already has a newer version of this document, updated for r0.2.1 with fixed DPV doc links. @AxelNennker You may want to consider merging your branch with master before merging the PR.