Release version 0.1.0

This is the first draft release of OpAMP spec.

What's Changed

• Add initial copy of OpAMP spec by @tigrannajaryan in #2
• Rename ErrorResponse to ServerErrorResponse by @tigrannajaryan in #10
• Add server_offered_version to AgentInstallStatus by @tigrannajaryan in #11
• Clarify generation of EffectiveConfig hash by @tigrannajaryan in #30
• Remove Health from Status Report message by @tigrannajaryan in #32
• Change addons and agent packages to only contain one downloadable file by @tigrannajaryan in #29
• Clarify OpAMP communication pattern by @tigrannajaryan in #35
• Add explanation of agent_attributes field by @tigrannajaryan in #34
• Add ability to indicate Capabilities in the protocol by @tigrannajaryan in #33
• Clarify Connection Establishment and Restoring by @tigrannajaryan in #36
• Support both HTTP 503 and 429 for throttling by @pmm-sumo in #37
• Eliminate DataForAgent message by @tigrannajaryan in #42
• Eliminate oneof Body from AgentToServer by @tigrannajaryan in #44
• Delete duplicate server_provided_all_addons_hash field by @tigrannajaryan in #45
• Add version field to Addons by @tigrannajaryan in #41
• Add capabilities field to ServerToAgent by @tigrannajaryan in #46
• Fix capabilities enum name and value by @tigrannajaryan in #47
• Generalize Agent identification by @tigrannajaryan in #48

Full Changelog: https://github.com/open-telemetry/opamp-spec/commits/v0.1.0