Host scrapers: Use same scrape time for all data points coming from same source

[james-bebbington]

Link to tracking Issue: #1271

Updated all metrics that come from the same source to use the same timestamp, calculated when scraping the system.

Note there are a couple of places where we get data from different sources within the same scraper which possibly indicates that these should be separated (will consider this change for a future PR):

1. network: Network Interface info is obtained separately from Connection Counts
2. swap: Swap / Page File Usage is obtained separately from Paging IO

(have not done process scraper yet, will do in a separate PR)

[codecov]

Codecov Report

Merging #1473 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1473      +/-   ##
==========================================
+ Coverage   90.92%   90.94%   +0.02%     
==========================================
  Files         239      239              
  Lines       16706    16728      +22     
==========================================
+ Hits        15190    15214      +24     
+ Misses       1085     1084       -1     
+ Partials      431      430       -1     

Impacted Files	Coverage Δ
...eceiver/internal/scraper/cpuscraper/cpu_scraper.go	100.00% <100.00%> (ø)
...r/internal/scraper/cpuscraper/cpu_scraper_linux.go	100.00% <100.00%> (ø)
...nternal/scraper/diskscraper/disk_scraper_others.go	100.00% <100.00%> (ø)
...l/scraper/diskscraper/disk_scraper_others_linux.go	100.00% <100.00%> (ø)
...al/scraper/filesystemscraper/filesystem_scraper.go	100.00% <100.00%> (ø)
...raper/filesystemscraper/filesystem_scraper_unix.go	100.00% <100.00%> (ø)
...eiver/internal/scraper/loadscraper/load_scraper.go	100.00% <100.00%> (+8.69%)	⬆️
...r/internal/scraper/memoryscraper/memory_scraper.go	100.00% <100.00%> (ø)
...rnal/scraper/memoryscraper/memory_scraper_linux.go	100.00% <100.00%> (ø)
...internal/scraper/networkscraper/network_scraper.go	98.46% <100.00%> (+0.02%)	⬆️
... and 5 more

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