chore: fixing broken links, updating to correct base url, replacing gitter with github discussions

[obecny]

more cleanups and fixes around links
removing gitter in favour of github discussions

[codecov]

Codecov Report

Merging #395 (0aed13c) into main (9aeec87) will increase coverage by 1.79%.
The diff coverage is n/a.

❗ Current head 0aed13c differs from pull request most recent head 9f5db32. Consider uploading reports for the commit 9f5db32 to get more accurate results

@@            Coverage Diff             @@
##             main     #395      +/-   ##
==========================================
+ Coverage   92.63%   94.43%   +1.79%     
==========================================
  Files           8       11       +3     
  Lines         285      431     +146     
  Branches       36       48      +12     
==========================================
+ Hits          264      407     +143     
- Misses         21       24       +3     

Impacted Files	Coverage Δ
...propagator-ot-trace/test/OTTracePropagator.test.ts	100.00% <0.00%> (ø)
...s/opentelemetry-propagator-ot-trace/src/version.ts	0.00% <0.00%> (ø)
...metry-propagator-ot-trace/src/OTTracePropagator.ts	95.83% <0.00%> (ø)

[dyladan]

Can we add a task like this to the lint?

[obecny]

Can we add a task like this to the lint?

#396