Document a workaround for using custom pagers on Windows

[stefanhaller]

Custom pagers are not supported on Windows, because using a pager in git requires the git command to run in a PTY, but the PTY package we are using doesn't support Windows.

However, there's a workaround to use a custom pager by using a Powershell script configured as an external diff command. Document this in the Custom_Pagers.md document, and export a LAZYGIT_COLUMNS environment variable to allow such scripts to work better.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for 4b59f981	✅ 0.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (4b59f98)	Report Missing	Report Missing	Report Missing
Head commit (2abd76e)	58232	50647	86.97%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#4941)	1	0	0.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

See your quality gate settings    Change summary preferences

Footnotes

1. Codacy didn't receive coverage data for the commit, or there was an error processing the received data. Check your integration for errors and validate that your coverage setup is correct. ↩