feat: add console table reporter

[Gazler]

The console table reporter will output a table to the console in the format:

      +--------------------------------------------+
      |                 vm.memory                  |
      +-------------+------------+----------+------+
      | Measurement | Type       | Value    | Tags |
      +-------------+------------+----------+------+
      | binary      | last_value | 100 byte | %{}  |
      | total       | counter    | 200      | %{}  |
      +-------------+------------+----------+------+

Currently, if the metric name is too long (the title) then it will be truncated. The following scenarios should probably also be considered:

1. Long measurement names
2. Long value names
3. Large tags
4. Fit to the terminal width

I'm not entirely sure how to tackle these scenarios, truncating seems like a reasonable solution for 1 and 2. For 3. Perhaps the tags could be rendered over multiple lines for simple values and a warning printed for longer values, such as the Plug.Conn in http requests.

[codecov-commenter]

Codecov Report

Merging #83 into master will decrease coverage by 0.09%. The diff coverage is 96.87%.

@@            Coverage Diff             @@
##           master      #83      +/-   ##
==========================================
- Coverage   97.11%   97.02%   -0.10%     
==========================================
  Files           2        3       +1     
  Lines         104      168      +64     
==========================================
+ Hits          101      163      +62     
- Misses          3        5       +2     

Flag	Coverage Δ
#1_10_otp21	97.00% <96.82%> (-0.11%)	:arrow_down:
#1_10_otp22	97.00% <96.82%> (-0.11%)	:arrow_down:
#1_6_otp19	96.96% <96.82%> (-0.09%)	:arrow_down:
#1_6_otp21	96.96% <96.82%> (-0.09%)	:arrow_down:

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Impacted Files	Coverage Δ
lib/telemetry_metrics/console_table_reporter.ex	96.87% <96.87%> (ø)

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[josevalim]

This looks great! As I mentioned to @Gazler, I am worried that the formatting will get wrecked in different situations though. For example, Phoenix includes the whole conn as metatags and if that's is accidentally included it will mess things up. One option though is to warn and exclude any tag that is not a atom/string/number.

[josevalim]

Closing this per the above. Thank you @Gazler.