Fix #6468 - Uses space match and adds newline for all sed flavors

[richmahn]

Fix for: #6468

This makes it so both GNU sed (Linux) and FreeBSD sed (MacOS) can be used for the sed commands used after the swagger command in make generate-swagger.

1. FreeBSD sed does not support \s so just a space is used now between basePath: and "/api/v1" as that all there will be.

2. For the new line at end of file, FreeBSD feels it should always add it, GNU sed does not. Easiest to add the -e '$a\' command which adds a new line at the end of a file if one doesn't already exist.

Before one could use homebrew to install GNU sed and rename gsed to sed, but now one can't. Also aliasing gsed to sed was not possible.

[codecov-io]

Codecov Report

Merging #6473 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6473      +/-   ##
==========================================
- Coverage    39.4%   39.39%   -0.01%     
==========================================
  Files         393      393              
  Lines       53271    53271              
==========================================
- Hits        20992    20988       -4     
- Misses      29292    29297       +5     
+ Partials     2987     2986       -1

Impacted Files	Coverage Δ
models/unit.go	0% <0%> (-14.29%)	⬇️
routers/repo/view.go	41.08% <0%> (-1%)	⬇️
models/repo_list.go	67.89% <0%> (+1.05%)	⬆️

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[zeripath]

I always feel it's a shame that bsd never takes obvious gnu improvements - or even proposes them to POSIX. It almost feels like a case of NIH.

Fine, I guess we need to do this.