Remove non-standard bold text from alerts in docs

Problem to solve

Should we allow all kinds of words in our alert boxes? The style guide does not state specifically that you can or can't do this. https://docs.gitlab.com/ee/development/documentation/styleguide.html#alert-boxes

Related to: !41377 (merged)

Further details

Style guide has CAUTION: **Caution:**.

• Use CAUTION or WARNING for Important.
• Use DANGER for Deprecated.

Variations of CAUTION in the docs:

CAUTION: **Deprecated:**
CAUTION: **Discontinued:**
CAUTION: **Warning:**
CAUTION: **Deprecation notice:**
CAUTION: **Important:**
CAUTION: **Attention:**
CAUTION: **Deprecation:**
CAUTION: **Planned Deprecation:**
CAUTION: **Two-factor authentication (2FA) is only supported with personal access tokens:**
CAUTION: **When updating the path of a user/group or transferring a (sub)group/project:**
CAUTION:**Caution:**
CAUTION: **WARNING:**
CAUTION: **Experimental:**
CAUTION: **IDE and Shell integrations:**

Style guide has NOTE: **Note:** only.

• Use CAUTION or WARNING for Important.
• Use DANGER for Deprecated.

Variations of NOTE in the docs:

Note: **NOTE:**
NOTE: **Alternative installation method:**
NOTE: **Deprecated:**
NOTE: **For GitLab employees:**
NOTE: **Important note:**
NOTE: **IMPORTANT:**
NOTE: **Important:**
NOTE: **Kubernetes experience required:**
NOTE: **Providing your own Redis instance:**
NOTE: **Tip:**

Style guide has TIP: **Tip:**. The style guide has no other variations for Tip. Maybe we should add Troubleshooting.

Variations of TIP in the docs:

TIP: **Troubleshooting:**
TIP: **Best practice:**
TIP: **If in doubt, choose Omnibus:**
TIP: **Learn more:**
TIP: **Payload size:**
TIP: **Troubleshooting:**

Style guide has DANGER: **Danger:**.

This variation is OK, according to the style guide.

Other variation in the docs:

DANGER: **Warning:**

Proposal

Who can address the issue

Other links/references