Add `er.showColumnTypes.related:` for showing related columns only

[k1LoW]

ref: #430

[github-actions[bot]]

Code Metrics Report

	main (8e77c4f)	#432 (1e24539)	+/-
Coverage	66.7%	65.2%	-1.4%
Code to Test Ratio	1:0.4	1:0.4	+0.0
Test Execution Time	3m12s	2m25s	-47s

Details

``` diff | | main (8e77c4f) | #432 (1e24539) | +/- | |---------------------|----------------|----------------|-------| - | Coverage | 66.7% | 65.2% | -1.4% | | Files | 35 | 35 | 0 | | Lines | 3408 | 3418 | +10 | - | Covered | 2272 | 2230 | -42 | + | Code to Test Ratio | 1:0.4 | 1:0.4 | +0.0 | | Code | 8878 | 8908 | +30 | + | Test | 3765 | 3835 | +70 | + | Test Execution Time | 3m12s | 2m25s | -47s | ```

Code coverage of files in pull request scope (60.0% → 63.9%)

Files	Coverage	+/-
config/config.go	69.9%	-1.6%
output/dot/dot.go	76.3%	0.0%
output/mermaid/mermaid.go	76.3%	0.0%
output/plantuml/plantuml.go	76.3%	0.0%
schema/schema.go	45.2%	+16.2%

---

Reported by octocov

[k1LoW]

@yasu89 Thank you for your review!!

[github-actions[bot]]

Code Metrics Report

	main (8e77c4f)	#432 (4633a58)	+/-
Coverage	66.7%	65.3%	-1.4%
Code to Test Ratio	1:0.4	1:0.4	+0.0
Test Execution Time	3m12s	2m22s	-50s

Details

``` diff | | main (8e77c4f) | #432 (4633a58) | +/- | |---------------------|----------------|----------------|-------| - | Coverage | 66.7% | 65.3% | -1.4% | | Files | 35 | 35 | 0 | | Lines | 3408 | 3416 | +8 | - | Covered | 2272 | 2230 | -42 | + | Code to Test Ratio | 1:0.4 | 1:0.4 | +0.0 | | Code | 8878 | 8903 | +25 | + | Test | 3765 | 3835 | +70 | + | Test Execution Time | 3m12s | 2m22s | -50s | ```

Code coverage of files in pull request scope (59.0% → 63.4%)

Files	Coverage	+/-
config/config.go	70.3%	-1.3%
output/mermaid/mermaid.go	76.3%	0.0%
output/plantuml/plantuml.go	76.3%	0.0%
schema/schema.go	45.2%	+16.2%

---

Reported by octocov