Add TSLint rule to enforce Apache headers in every file

[rochdev]

Is your feature request related to a problem? Please describe.

As discussed in #33, the license should be added automatically to every file to avoid users forgetting to add it, or add it in an inconsistent way.

Describe the solution you'd like

TSLint can be used for this purpose with the file-header rule. The header should also be reduced to a minimal copyright notice to avoid polluting every file with a large block of license at the top.

Describe alternatives you've considered

Alternatively, we could use a license that doesn't strongly suggest a per-file license. Unfortunately, right now Apache-2.0 is enforced by CNCF so this will need to be discussed outside the scope of this project.

[rochdev]

@caniszczyk @bogdandrutu Could you confirm what a minimal one-liner license would look like as discussed in open-telemetry/community#113?

[caniszczyk]

sorry something like:

// Copyright OpenTelemetry Contributors. SPDX-License-Identifier: Apache-2.0

[mayurkale22]

// Copyright OpenTelemetry Contributors. SPDX-License-Identifier: Apache-2.0

@draffensperger FYI

[draffensperger]

@mayurkale22 did you get official confirmation from CNCF folks that this short form header is allowed?

[OlivierAlbertini]

Any news on this issue ? I'm waiting to merge this one for doing #165