Add progress bar during query execution to track progress.

[sokolcati]

Progress bar is run-time SQL-query progress indicator.

Function pg_progress_bar(pid) extracts the current query state from backend with specified 'pid'. Then gets the numerical values of the actual rows and total rows and count progress for the whole query tree. Function returns numeric value from 0 to 1 describing the measure of query fulfillment. This function can be used to be embedded in the PostgreSQL GUI.

To intuitively track progress without using a graphical client, you can use the additionally implemented function pg_progress_bar_visual(pid, delay). It prints state every period specified by 'delay' (in seconds).

Increase version to 1.2 due to init.sql change.

[codecov]

Codecov Report

Attention: Patch coverage is 69.17808% with 45 lines in your changes missing coverage. Please review.

Project coverage is 87.21%. Comparing base (5dec7d4) to head (29fd922).

Files with missing lines	Patch %	Lines
pg_query_state.c	69.17%	45 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #59      +/-   ##
==========================================
- Coverage   90.90%   87.21%   -3.70%     
==========================================
  Files          10       10              
  Lines         748      884     +136     
==========================================
+ Hits          680      771      +91     
- Misses         68      113      +45     

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