chore(license): update source code headers + copyright year

[wass3rw3rk]

ref: go-vela/community#747

• replaces code file license headers with SPDX header (see https://spdx.dev/ids/#why); this removes copyright + year
• update golangci-lint rule to ensure code file enforcement
• use first commit date for copyright year and updates year in other select places
• format is changed to match "Copyright [yyyy] [name of copyright owner]" as shown here: https://www.apache.org/licenses/LICENSE-2.0.html

[codecov]

Codecov Report

Merging #57 (44dd888) into main (290af6c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #57   +/-   ##
=======================================
  Coverage   93.47%   93.47%           
=======================================
  Files           3        3           
  Lines         291      291           
=======================================
  Hits          272      272           
  Misses         13       13           
  Partials        6        6           

Files Changed	Coverage Δ
internal/scp/scp.go	92.10% <ø> (ø)
internal/ssh/ssh.go	91.66% <ø> (ø)
pkg/binarywrapper/binarywrapper.go	98.55% <ø> (ø)

[KellyMerrick]

lgtm