Refactor slack and teams notifications

[kingzacko1]

refactor of the Slack and Teams notification types code to more closely align with use of AutoValue across the project. There should be no functional difference in the two notifications.

Notes for Reviewers

• The commit history must be preserved - please use the rebase-merge or standard merge option instead of squash-merge
• Sync up with the author before merging

[ryan-carroll-graylog]

Everything looks good to me code wise (minus one possible log message update in comment). The original functionality is working in testing for both notification types.

This is not in the original scope of this PR, but I did notice an existing bug where you can use a teams webhook for a slack notification and vice versa. If you think it's worth fixing in this PR I believe modifying the nested if statements in the validate() methods of following files should fix the issue:

graylog-plugin-integrations/src/main/java/org/graylog/integrations/notifications/types/SlackEventNotificationConfig.java

Lines 125 to 130 in 07ca26e

	if (webhookUri.getHost().toLowerCase().contains("slack")) {
	if (!SLACK_PATTERN.matcher(webhookUrl()).find()) {
	validation.addError(FIELD_WEBHOOK_URL, INVALID_SLACK_URL_ERROR_MESSAGE);
	}
	} else if (webhookUri.getHost().toLowerCase().contains("discord")) {
	if (!DISCORD_PATTERN.matcher(webhookUrl()).find()) {

graylog-plugin-integrations/src/main/java/org/graylog/integrations/notifications/types/microsoftteams/TeamsEventNotificationConfig.java

Lines 97 to 98 in 07ca26e

	if (webhookUri.getHost().toLowerCase().contains("office")) {
	if (!TEAMS_PATTERN.matcher(webhookUrl()).find()) {

[kingzacko1]

Fixed the log message and updated URL validation logic in latest commit @ryan-carroll-graylog

[roberto-graylog]

Looks good.

[danotorrey]

Thank you @kingzacko1!