docs: New fallback_sitrep() and related functionality for collecting telemetry data

[krlmlr]

Collection and uploading of fallback events are now a two-step process. At run time, events are written to an .ndjson file, one line per entry, one file per process, anonymized. All entries can be reviewed with the new fallback_review() and deleted with fallback_purge() . The new fallback_upload() then uploads the collected data. Uploading can also happen during package load (opt-in).

The new fallback_sitrep() gives a situation report about the configuration and the available reports.

Closes #102.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 43.31210% with 89 lines in your changes are missing coverage. Please review.

Project coverage is 9.59%. Comparing base (2438c2b) to head (f407bf0).

❗ Current head f407bf0 differs from pull request most recent head 8d938cc. Consider uploading reports for the commit 8d938cc to get more accurate results

Files	Patch %	Lines
R/fallback.R	40.90%	52 Missing ⚠️
R/telemetry.R	45.58%	37 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff            @@
##            main    #111      +/-   ##
========================================
+ Coverage   9.35%   9.59%   +0.23%     
========================================
  Files        128     129       +1     
  Lines      22463   22620     +157     
========================================
+ Hits        2102    2170      +68     
- Misses     20361   20450      +89     

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