chore: Update CHANGELOG implementation

[embano1]

Description

This PR updates the CHANGELOG and release notes generation process and layout:

• Use different templates for release notes (shown in Github Release) and CHANGELOG.md
  • Release notes will now include issue references in commit lines (when available, detected with Closes or Fixes pattern matching)
  • CHANGELOG.md will not include issue references in output
• Include additional highlights for documentation, examples, and bug fixes
• Update CONTRIBUTING guide to explain how to use these prefixes
• Add BREAKING changes section to release notes/CHANGELOG, detected when using BREAKING: in commit message body
• Build, Docker login and release workflow can now be triggered manually (dispach)
• Updated CHANGELOG.md with changes
• CHANGELOG.md as part of a release does not have to be created manually anymore (bot will create PR)

Closes: #2467
Signed-off-by: Michael Gasch mgasch@vmware.com

Example of rendered Release Notes

Release v0.26.0

Release Date: 2021-05-28

🐞 Fix

• [70b92d6] Isolate SSO govc tests (Fix govc tests #2425)

💡 Examples

• [81b1de1] add toolbox Client.Run (How I can do run code in vm, without govc ? #2458)

💫 govc (CLI)

• [e37e515] fix default guest.run path for unsupported Windows guests (Executing file on windows vm using govc #2446)
• [0e7012d] Add support for getting the VC proxy and no-proxy configuration (#2435) (govc: Add support for getting the VC proxy and no-proxy configuration #2435)
• [6afb8ff] Change 'Maintenance Mode' printing in host.info (host.info printing "Maintenance Mode" without new line #2398)

💫 vcsim (Simulator)

• [0c0ed98] fix race in CloneVM_Task
• [d01d0fa] add simulator.RunContainer method
• [8ab0c99] untie datastore capacity from local fs (vcsim should provide a way to set the initial capacity for a datastore #2390)
• [d31941c] Modify Usage of README. (based on v0.25.0)
• [4fea687] include all namespaces in /about info
• [bd3467d] avoid edit device panic when DeviceInfo is nil
• [35a42af] add guest operations process support

📃 Documentation

• [1f795d2] Add blog to vcsim README
• [2719c22] Document linker and GOFLAGS for build vars (govc version says 0.0.0 #2401)

Example highlighting Breaking Changes

⚠️ BREAKING

remove ctx from param

func (removed context.Context) error {...}

Type of change

Please mark options that are relevant:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide
instructions so we can reproduce. If applicable, please also list any relevant
details for your test configuration.

• Test Description 1
• Test Description 2

Test Configuration:

• Toolchain:
• SDK:
• (add more if needed)

Checklist:

• My code follows the CONTRIBUTION guidelines of
  this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

[dougm]

Awesome @embano1