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 #318 (93e9796) into main (feb196d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #318   +/-   ##
=======================================
  Coverage   97.08%   97.08%           
=======================================
  Files          62       62           
  Lines        6816     6816           
=======================================
  Hits         6617     6617           
  Misses        147      147           
  Partials       52       52           

Files Changed	Coverage Δ
database/build.go	100.00% <ø> (ø)
database/build_executable.go	92.59% <ø> (ø)
database/build_queue.go	100.00% <ø> (ø)
database/compression.go	57.14% <ø> (ø)
database/context.go	100.00% <ø> (ø)
database/encryption.go	82.35% <ø> (ø)
database/hook.go	100.00% <ø> (ø)
database/log.go	91.66% <ø> (ø)
database/pipeline.go	94.64% <ø> (ø)
database/repo.go	98.25% <ø> (ø)
... and 52 more

[wass3rw3rk]

will recreate