Add support for database SSL verification and encryption

[enarha]

Changes

A configuration option for setting database SSL mode existed, but there was no support for using custom CA certificates. A new option was added to allow the user to set path for CA cert to be used for validation and encryption.

/kind feature

fixes #531

Submitter Checklist

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• [x] Has Docs included if any changes are user facing
• [ ] Has Tests included if any functionality added or changed
• [x] Tested your changes locally (if this is a code change)
• [x] Follows the commit message standard
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Release Notes

A new configuration option DB_SSLROOTCERT was added with a default value of empty string. You do not need to set that value, unless you want to enforce TLS connection to your database and use custom CA certificate for it.

[tekton-robot]

The following is the coverage report on the affected files. Say /test pull-tekton-results-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
cmd/api/main.go	12.1%	11.9%	-0.2

[tekton-robot]

The following is the coverage report on the affected files. Say /test pull-tekton-results-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
cmd/api/main.go	12.1%	11.9%	-0.2

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: avinal, iainsproat, sayan-biswas

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/tektoncd/results/blob/main/OWNERS)~~ [avinal,sayan-biswas] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[tekton-robot]

The following is the coverage report on the affected files. Say /test pull-tekton-results-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
cmd/api/main.go	12.1%	11.9%	-0.2

[avinal]

Got approval from all the reviewers. Moving forward /lgtm