Add fallback strategy to get MM team

[mszostok]

Description

Changes proposed in this pull request:

• Add fallback strategy to get MM team

Testing

When you're running Botkube against the MM docker image mattermost/mattermost-preview it does not work as they don't have the search team endpoint implemented. So this change allows using the GetTeam as a fallback strategy.

You can test it by following those instructions: https://github.com/mattermost/mattermost-bot-sample-golang/tree/master

and later doing the same but with a helm chart:

$ helm repo add mattermost https://helm.mattermost.com
$ helm install mattermost/mattermost-team-edition \
  --set mysql.mysqlUser=sampleUser \
  --set mysql.mysqlPassword=samplePassword \

[pkosiec]

LGTM
Disclaimer: I did just the code review.

[pkosiec]

Should we handle a case when there are multiple botTeams? Maybe return an error that we found multiple (printing theirs name + displayName)?