Moved discovery client implementation into his own library

Please check if the PR fulfills these requirements

[X] The PR has no duplicates (please search among the Pull Requests before creating one)
[X] The PR follows our contributing guidelines
[X] Tests for the changes have been added (for bug fixes / features)
[ ] Docs have been added / updated (for bug fixes / features)
[ ] UPGRADING.md has been updated with a migration guide (for breaking changes)
[ ] configuration.schema.json updated if new parameters are added.

What kind of change does this PR introduce?

Moved the pluggable discovery client implementation in the pluggable-discovery-protocol-handler/v2 library. This change provides two benefits:

It greatly simplifies the Arduino CLI codebase.
The discovery client code can be reused in other projects

What is the current behavior?

No changes.

What is the new behavior?

Does this PR introduce a breaking change, and is titled accordingly?

Other information

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (2b2394e) 68.95% compared to head (c5e66f5) 69.39%. Report is 1 commits behind head on master.

Files	Patch %	Lines
commands/upload/upload.go	66.66%	0 Missing and 1 partial :warning:
...ino/discovery/discoverymanager/discoverymanager.go	91.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2531 +/- ## ========================================== + Coverage 68.95% 69.39% +0.43% ========================================== Files 204 202 -2 Lines 20535 20110 -425 ========================================== - Hits 14160 13955 -205 + Misses 5220 5035 -185 + Partials 1155 1120 -35 ``` | [Flag](https://app.codecov.io/gh/arduino/arduino-cli/pull/2531/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=arduino) | Coverage Δ | | |---|---|---| | [unit](https://app.codecov.io/gh/arduino/arduino-cli/pull/2531/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=arduino) | `69.39% <89.47%> (+0.43%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=arduino#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

arduino / arduino-cli