Description

This pull request adds ES 7.x support in Bosun.
I submitted #2427 before but that is based on my own go modules migration pull request which is different from what upstream maintainers did. This one is based on upstream go modules migration.

• https://github.com/olivere/elastic/ version 7 client is used.
• Most code are copy-pasted from ES version 6 support.
• The one difference is in ES 7 mapping types is removed, Type(docType) are removed in ES7

Type of change

From the following, please check the 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?

Tested with ES 7.2 and also ES 6.8 to make sure nothing breaks.

• update the configuration toml file and create some alerts to query ES
• verify alerts can be triggered and no errors in ES query
• verify annotate can work

Checklist:

• This contribution follows the project's code of conduct
• This contribution follows the project's contributing guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• 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 and published in downstream modules